Note: Descriptions are shown in the official language in which they were submitted.
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HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK
Field of the Invention
[0001] The present invention relates to processes for hydromethanating a
carbonaceous
feedstock to a methane-enriched synthesis gas, where an oxygen-rich gas stream
and the
carbonaceous feedstock are fed into a fluidized-bed hydromethanation reactor,
and where the
carbonaceous feedstock as fed into the hydromethanation reactor has an
elevated moisture
content in order, for example, to assist in heat management within the
hydromethanation
reactor.
Background of the Invention
[0002] In view of numerous factors such as higher energy prices and
environmental
concerns, the production of value-added products (such as pipeline-quality
substitute natural
gas, hydrogen, methanol, higher hydrocarbons, ammonia and electrical power)
from lower-
fuel-value carbonaceous feedstocks (such as petroleum coke, resids,
asphaltenes, coal and
biomass) is receiving renewed attention.
[0003] Such lower-fuel-value carbonaceous feedstocks can be gasified at
elevated
temperatures and pressures to produce a synthesis gas stream that can
subsequently be
converted to such value-added products.
[0004] One advantageous gasification process is hydromethanation, in which the
carbonaceous feedstock is converted in a fluidized-bed hydromethanation
reactor in the
presence of a catalyst source and steam at moderately-elevated temperatures
and pressures to
directly produce a methane-rich synthesis gas stream (medium BTU synthesis gas
stream)
raw product. This is distinct from conventional gasification processes, such
as those based on
partial combustion/oxidation of a carbon source at highly-elevated
temperatures and
pressures (thermal gasification, typically non-catalytic), where a syngas
(carbon monoxide +
hydrogen) is the primary product (little or no methane is directly produced),
which can then
be further processed to produce methane (via catalytic methanation, see
reaction (III) below)
or any number of other higher hydrocarbon products.
[0005] Hydromethanation processes and the conversion/utilization of the
resulting methane-
rich synthesis gas stream to produce value-added products are disclosed, for
example, in
U53 828474, U53 958957, U53998607, US4057512, US4092125, U54094650, U54204843,
U54243639, U54468231, U54500323, U54541841, U54551155, U54558027, U54606105,
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US4617027, US4609456, US5017282, US5055181, US6187465, US6790430, US6894183,
US6955695, US2003/0167961A1, US2006/0265953A1,
US2007/000177A1,
US2007/083072A1, US2007/0277437A1, US2009/0048476A1, US2009/0090056A1,
US2009/0090055A1, US2009/0165383A1, US2009/0166588A1, US2009/0165379A1,
US2009/0170968A1, US2009/0165380A1, US2009/0165381A1, US2009/0165361A1,
US2009/0165382A1, US2009/0169449A1, US2009/0169448A1, US2009/0165376A1,
US2009/0165384A1, US2009/0217582A1, US2009/0220406A1, US2009/0217590A1,
US2009/0217586A1, US2009/0217588A1, US2009/0218424A1, US2009/0217589A1,
US2009/0217575A1, US2009/0229182A1, US2009/0217587A1, US2009/0246120A1,
US2009/0259080A1, US2009/0260287A1, US2009/0324458A1, US2009/0324459A1,
US2009/0324460A1, US2009/0324461A1, US2009/0324462A1, US2010/0071235A1,
US2010/0071262A1, US2010/0120926A1, US2010/0121125A1, US2010/0168494A1,
US2010/0168495A1, US2010/0179232A1, US2010/0287835A1, US2011/0031439A1,
US2011/0062012A1, US2011/0062722A1, US2011/0062721A1, US2011/0064648A1,
US2011/0088896A1, US2011/0088897A1, US2011/0146978A1, US2011/0146979A1,
US2011/0207002A1, US2011/0217602A1 and GB1599932. See also Chiaramonte et al,
"Upgrade Coke by Gasification", Hydrocarbon Processing, Sept. 1982, pp. 255-
257; and
Kalina et al, "Exxon Catalytic Coal Gasification Process Predevelopment
Program, Final
Report", Exxon Research and Engineering Co., Baytown, TX, FE236924, December
1978.
[0006] The hydromethanation of a carbon source typically involves four
theoretically
separate reactions:
[0007] Steam carbon: C + H2O -> CO + H2 (I)
[0008] Water-gas shift: CO + H20 -> H2 CO2 (II)
[0009] CO Methanation: C0+3H2 -> CH4 + H20 (III)
[0010] Hydro-gasification: 2H2 + C -> CH4 (IV)
[0011] In the hydromethanation reaction, the first three reactions (I-III)
predominate to result
in the following overall reaction:
[0012] 2C + 2H20 -> CH4 + CO2 (V).
[0013] The overall hydromethanation reaction is essentially thermally
balanced; however,
due to process heat losses and other energy requirements (such as required for
evaporation of
moisture entering the reactor with the feedstock), some heat must be added to
maintain the
thermal balance.
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[0014] The reactions are also essentially syngas (hydrogen and carbon
monoxide) balanced
(syngas is produced and consumed); therefore, as carbon monoxide and hydrogen
are
withdrawn with the product gases, carbon monoxide and hydrogen need to be
added to the
reaction as required to avoid a deficiency.
[0015] In order to maintain the net heat of reaction as close to neutral as
possible (only
slightly exothermic or endothermic), and maintain the syngas balance, a
superheated gas
stream of steam, carbon monoxide and hydrogen is often fed to the
hydromethanation reactor.
Frequently, the carbon monoxide and hydrogen streams are recycle streams
separated from
the product gas, and/or are provided by reforming/partially oxidating a
portion of the product
methane. See, for
example, previously incorporated U54094650, U56955595 and
U52007/083072A1.
[0016] In one variation of the hydromethanation process, required carbon
monoxide,
hydrogen and heat energy can also at least in part be generated in situ by
feeding oxygen into
the hydromethanation reactor. See, for
example, previously incorporated
U52010/0076235A1 and U52010/0287835A1, as well as commonly-owned US Patent
Application Ser. No. 13/211,476 (attorney docket no. FN-0063 US NP1, entitled
HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK), which was filed 17 August 2011;
and commonly-owned US Provisional Application Ser. No. 13/228,821 (attorney
docket no.
FN-0064 US NP1, entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK), which
was filed 9 September 2011.
[0017] The result is a "direct" methane-enriched raw product gas stream also
containing
substantial amounts of hydrogen, carbon monoxide and carbon dioxide which can,
for
example, be directly utilized as a medium BTU energy source, or can be
processed to result
in a variety of higher-value product streams such as pipeline-quality
substitute natural gas,
high-purity hydrogen, methanol, ammonia, higher hydrocarbons, carbon dioxide
(for
enhanced oil recovery and industrial uses) and electrical energy.
[0018] In the variation of the hydromethanation process mentioned above, where
oxygen is
fed into the reactor to generate required carbon monoxide, hydrogen and heat
energy for the
hydromethanation reaction, one of the primary concerns is the formation of hot
spots, and
control and distribution of the heat energy produced as a result of the
oxidation reaction.
Poor heat management in the hydromethanation reactor can, for example, result
in premature
(and sometimes catastrophic) equipment failure, as well as agglomeration of
carbonaceous
materials.
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[0019] Addressing the issue of heat management in the hydromethanation reactor
is,
therefore, a critical issue to the proper operation and optimization of the
hydromethanation
process, and the present invention provides one solution to the heat
management issue.
Summary of the Invention
[0020] In one aspect, the invention provides a process for generating a
methane-enriched raw
product gas stream from a non-gaseous carbonaceous material, the process
comprising the
steps of:
[0021] (a) supplying to a hydromethanation reactor
[0022] (1) a carbonaceous feedstock derived from the non-gaseous
carbonaceous
material,
[0023] (2) a hydromethanation catalyst,
[0024] (3) a superheated steam stream and
[0025] (4) an oxygen-rich gas stream,
[0026] wherein the hydromethanation reactor comprises a fluidized bed having a
upper
portion above a lower portion, and wherein the superheated steam stream and
the oxygen-rich
gas stream are introduced into the lower portion of the fluidized bed;
[0027] (b) reacting a portion of the carbonaceous feedstock in the
hydromethanation reactor
in the presence of hydromethanation catalyst, carbon monoxide, hydrogen and
steam at a
target operating temperature to produce a methane-enriched raw gas and a solid
by-product
char, wherein the methane-enriched raw gas comprises methane, carbon monoxide,
hydrogen,
carbon dioxide, hydrogen sulfide, steam, heat energy and entrained fines; and
[0028] (c) reacting a portion of the carbonaceous feedstock with oxygen to
produce carbon
monoxide, hydrogen and heat energy;
[0029] wherein:
[0030] (i) the reaction of step (b) predominates in the upper portion of
the fluidized
bed;
[0031] (ii) the reaction of step (c) predominates in the lower portion of
the fluidized
bed; and
[0032] (iii) the carbonaceous feedstock as supplied to the hydromethanation
reactor
comprises contains an elevated moisture content of from greater than 10 wt%
to about 25 wt% (based on the total weight of the carbonaceous feedstock), to
the extent that the carbonaceous feedstock is substantially free-flowing.
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[0033] The process in accordance with the present invention is useful, for
example, for
producing higher-value products and by-products from various carbonaceous
materials.
[0034] In addition to the heat management issue, the ability to feed higher
moisture content
carbonaceous feedstock into the hydromethanation increases overall efficiency
of the process
due, for example, to the reduction of drying that may be necessary in the
feedstock
preparation, as discussed in further detail below.
[0035] These and other embodiments, features and advantages of the present
invention will
be more readily understood by those of ordinary skill in the art from a
reading of the
following detailed description.
Brief Description of the Drawings
[0036] Figure 1 is a diagram of an embodiment of the process for generating a
methane-
enriched raw product gas stream in accordance with the present invention.
[0037] Figure 2 is a diagram of an embodiment for the further processing of a
methane-
enriched raw product stream to generate one or more value-added products such
as hydrogen,
substitute natural gas and/or electrical power.
Detailed Description
[0038] The present invention relates to processes for converting a non-gaseous
carbonaceous
material ultimately into one or more value-added gaseous products. Further
details are
provided below.
[0039] In the context of the present description, all publications, patent
applications, patents
and other references mentioned herein, if not otherwise indicated, are
explicitly incorporated
by reference herein in their entirety for all purposes as if fully set forth.
[0040] Unless otherwise defined, all technical and scientific terms used
herein have the same
meaning as commonly understood by one of ordinary skill in the art to which
this disclosure
belongs. In case of conflict, the present specification, including
definitions, will control.
[0041] Except where expressly noted, trademarks are shown in upper case.
[0042] Unless stated otherwise, all percentages, parts, ratios, etc., are by
weight.
[0043] Unless stated otherwise, pressures expressed in psi units are gauge,
and pressures
expressed in kPa units are absolute.
[0044] When an amount, concentration, or other value or parameter is given as
a range, or a
list of upper and lower values, this is to be understood as specifically
disclosing all ranges
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formed from any pair of any upper and lower range limits, regardless of
whether ranges are
separately disclosed. Where a range of numerical values is recited herein,
unless otherwise
stated, the range is intended to include the endpoints thereof, and all
integers and fractions
within the range. It is not intended that the scope of the present disclosure
be limited to the
specific values recited when defining a range.
[0045] When the term "about" is used in describing a value or an end-point of
a range, the
disclosure should be understood to include the specific value or end-point
referred to.
[0046] As used herein, the terms "comprises," "comprising," "includes,"
"including," "has,"
"having" or any other variation thereof, are intended to cover a non-exclusive
inclusion. For
example, a process, method, article, or apparatus that comprises a list of
elements is not
necessarily limited to only those elements but can include other elements not
expressly listed
or inherent to such process, method, article, or apparatus.
[0047] Further, unless expressly stated to the contrary, "or" and "and/or"
refers to an
inclusive and not to an exclusive. For example, a condition A or B, or A
and/or B, is satisfied
by any one of the following: A is true (or present) and B is false (or not
present), A is false
(or not present) and B is true (or present), and both A and B are true (or
present).
[0048] The use of "a" or "an" to describe the various elements and components
herein is
merely for convenience and to give a general sense of the disclosure. This
description should
be read to include one or at least one and the singular also includes the
plural unless it is
obvious that it is meant otherwise.
[0049] The term "substantial", as used herein, unless otherwise defined
herein, means that
greater than about 90% of the referenced material, preferably greater than
about 95% of the
referenced material, and more preferably greater than about 97% of the
referenced material.
If not specified, the percent is on a molar basis when reference is made to a
molecule (such as
methane, carbon dioxide, carbon monoxide and hydrogen sulfide), and otherwise
is on a
weight basis (such as for entrained fines).
[0050] The term "predominant portion", as used herein, unless otherwise
defined herein,
means that greater than 50% of the referenced material. If not specified, the
percent is on a
molar basis when reference is made to a molecule (such as hydrogen, methane,
carbon
dioxide, carbon monoxide and hydrogen sulfide), and otherwise is on a weight
basis (such as
for entrained fines).
[0051] The term "depleted" is synonymous with reduced from originally present.
For
example, removing a substantial portion of a material from a stream would
produce a
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material-depleted stream that is substantially depleted of that material.
Conversely, the term
"enriched" is synonymous with greater than originally present.
[0052] The term "carbonaceous" as used herein is synonymous with hydrocarbon.
[0053] The term "carbonaceous material" as used herein is a material
containing organic
hydrocarbon content. Carbonaceous materials can be classified as biomass or
non-biomass
materials as defined herein.
[0054] The term "biomass" as used herein refers to carbonaceous materials
derived from
recently (for example, within the past 100 years) living organisms, including
plant-based
biomass and animal-based biomass. For clarification, biomass does not include
fossil-based
carbonaceous materials, such as coal. For
example, see previously incorporated
US2009/0217575A1, US2009/0229182A1 and US2009/0217587A1.
[0055] The term "plant-based biomass" as used herein means materials derived
from green
plants, crops, algae, and trees, such as, but not limited to, sweet sorghum,
bagasse, sugarcane,
bamboo, hybrid poplar, hybrid willow, albizia trees, eucalyptus, alfalfa,
clover, oil palm,
switchgrass, sudangrass, millet, jatropha, and miscanthus (e.g., Miscanthus x
giganteus).
Biomass further include wastes from agricultural cultivation, processing,
and/or degradation
such as corn cobs and husks, corn stover, straw, nut shells, vegetable oils,
canola oil,
rapeseed oil, biodiesels, tree bark, wood chips, sawdust, and yard wastes.
[0056] The term "animal-based biomass" as used herein means wastes generated
from
animal cultivation and/or utilization. For example, biomass includes, but is
not limited to,
wastes from livestock cultivation and processing such as animal manure, guano,
poultry litter,
animal fats, and municipal solid wastes (e.g., sewage).
[0057] The term "non-biomass", as used herein, means those carbonaceous
materials which
are not encompassed by the term "biomass" as defined herein. For example, non-
biomass
include, but is not limited to, anthracite, bituminous coal, sub-bituminous
coal, lignite,
petroleum coke, asphaltenes, liquid petroleum residues or mixtures thereof For
example, see
US2009/0166588A1, US2009/0165379A1, US2009/0165380A1, US2009/0165361A1,
US2009/0217590A1 and US2009/0217586A1.
[0058] "Liquid heavy hydrocarbon materials" are viscous liquid or semi-solid
materials that
are flowable at ambient conditions or can be made flowable at elevated
temperature
conditions. These materials are typically the residue from the processing of
hydrocarbon
materials such as crude oil. For example, the first step in the refining of
crude oil is normally
a distillation to separate the complex mixture of hydrocarbons into fractions
of differing
volatility. A typical first-step distillation requires heating at atmospheric
pressure to vaporize
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as much of the hydrocarbon content as possible without exceeding an actual
temperature of
about 650 F, since higher temperatures may lead to thermal decomposition. The
fraction
which is not distilled at atmospheric pressure is commonly referred to as
"atmospheric
petroleum residue". The fraction may be further distilled under vacuum, such
that an actual
temperature of up to about 650 F can vaporize even more material. The
remaining
undistillable liquid is referred to as "vacuum petroleum residue". Both
atmospheric
petroleum residue and vacuum petroleum residue are considered liquid heavy
hydrocarbon
materials for the purposes of the present invention.
[0059] Non-limiting examples of liquid heavy hydrocarbon materials include
vacuum resids;
atmospheric resids; heavy and reduced petroleum crude oils; pitch, asphalt and
bitumen
(naturally occurring as well as resulting from petroleum refining processes);
tar sand oil;
shale oil; bottoms from catalytic cracking processes; coal liquefaction
bottoms; and other
hydrocarbon feedstreams containing significant amounts of heavy or viscous
materials such
as petroleum wax fractions.
[0060] The term "asphaltene" as used herein is an aromatic carbonaceous solid
at room
temperature, and can be derived, for example, from the processing of crude oil
and crude oil
tar sands. Asphaltenes may also be considered liquid heavy hydrocarbon
feedstocks.
[0061] The liquid heavy hydrocarbon materials may inherently contain minor
amounts of
solid carbonaceous materials, such as petroleum coke and/or solid asphaltenes,
that are
generally dispersed within the liquid heavy hydrocarbon matrix, and that
remain solid at the
elevated temperature conditions utilized as the feed conditions for the
present process.
[0062] The terms "petroleum coke" and "petcoke" as used herein include both
(i) the solid
thermal decomposition product of high-boiling hydrocarbon fractions obtained
in petroleum
processing (heavy residues ¨ "resid petcoke"); and (ii) the solid thermal
decomposition
product of processing tar sands (bituminous sands or oil sands ¨ "tar sands
petcoke"). Such
carbonization products include, for example, green, calcined, needle and
fluidized bed
petcoke.
[0063] Resid petcoke can also be derived from a crude oil, for example, by
coking processes
used for upgrading heavy-gravity residual crude oil (such as a liquid
petroleum residue),
which petcoke contains ash as a minor component, typically about 1.0 wt% or
less, and more
typically about 0.5 wt% of less, based on the weight of the coke. Typically,
the ash in such
lower-ash cokes predominantly comprises metals such as nickel and vanadium.
[0064] Tar sands petcoke can be derived from an oil sand, for example, by
coking processes
used for upgrading oil sand. Tar sands petcoke contains ash as a minor
component, typically
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in the range of about 2 wt% to about 12 wt%, and more typically in the range
of about 4 wt%
to about 12 wt%, based on the overall weight of the tar sands petcoke.
Typically, the ash in
such higher-ash cokes predominantly comprises materials such as silica and/or
alumina.
[0065] Petroleum coke can comprise at least about 70 wt% carbon, at least
about 80 wt%
carbon, or at least about 90 wt% carbon, based on the total weight of the
petroleum coke.
Typically, the petroleum coke comprises less than about 20 wt% inorganic
compounds, based
on the weight of the petroleum coke.
[0066] The term "coal" as used herein means peat, lignite, sub-bituminous
coal, bituminous
coal, anthracite, or mixtures thereof In certain embodiments, the coal has a
carbon content
of less than about 85%, or less than about 80%, or less than about 75%, or
less than about
70%, or less than about 65%, or less than about 60%, or less than about 55%,
or less than
about 50% by weight, based on the total coal weight. In other embodiments, the
coal has a
carbon content ranging up to about 85%, or up to about 80%, or up to about 75%
by weight,
based on the total coal weight. Examples of useful coal include, but are not
limited to, Illinois
#6, Pittsburgh #8, Beulah (ND), Utah Blind Canyon, and Powder River Basin
(PRB) coals.
Anthracite, bituminous coal, sub-bituminous coal, and lignite coal may contain
about 10
wt%, from about 5 to about 7 wt%, from about 4 to about 8 wt%, and from about
9 to about
11 wt%, ash by total weight of the coal on a dry basis, respectively. However,
the ash
content of any particular coal source will depend on the rank and source of
the coal, as is
familiar to those skilled in the art. See, for example, "Coal Data: A
Reference", Energy
Information Administration, Office of Coal, Nuclear, Electric and Alternate
Fuels, U.S.
Department of Energy, DOE/EIA-0064(93), February 1995.
[0067] The ash produced from combustion of a coal typically comprises both a
fly ash and a
bottom ash, as is familiar to those skilled in the art. The fly ash from a
bituminous coal can
comprise from about 20 to about 60 wt% silica and from about 5 to about 35 wt%
alumina,
based on the total weight of the fly ash. The fly ash from a sub-bituminous
coal can comprise
from about 40 to about 60 wt% silica and from about 20 to about 30 wt%
alumina, based on
the total weight of the fly ash. The fly ash from a lignite coal can comprise
from about 15 to
about 45 wt% silica and from about 20 to about 25 wt% alumina, based on the
total weight of
the fly ash. See, for example, Meyers, et al. "Fly Ash. A Highway Construction
Material,"
Federal Highway Administration, Report No. FHWA-IP-76-16, Washington, DC,
1976.
[0068] The bottom ash from a bituminous coal can comprise from about 40 to
about 60 wt%
silica and from about 20 to about 30 wt% alumina, based on the total weight of
the bottom
ash. The bottom ash from a sub-bituminous coal can comprise from about 40 to
about 50
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wt% silica and from about 15 to about 25 wt% alumina, based on the total
weight of the
bottom ash. The bottom ash from a lignite coal can comprise from about 30 to
about 80 wt%
silica and from about 10 to about 20 wt% alumina, based on the total weight of
the bottom
ash. See, for example, Moulton, Lyle K. "Bottom Ash and Boiler Slag,"
Proceedings of the
Third International Ash Utilization Symposium, U.S. Bureau of Mines,
Information Circular
No. 8640, Washington, DC, 1973.
[0069] A material such as methane can be biomass or non-biomass under the
above
definitions depending on its source of origin.
[0070] A "non-gaseous" material is substantially a liquid, semi-solid, solid
or mixture at
ambient conditions. For example, coal, petcoke, asphaltene and liquid
petroleum residue are
non-gaseous materials, while methane and natural gas are gaseous materials.
[0071] The term "unit" refers to a unit operation. When more than one "unit"
is described as
being present, those units are operated in a parallel fashion unless otherwise
stated. A single
"unit", however, may comprise more than one of the units in series, or in
parallel, depending
on the context. For example, an acid gas removal unit may comprise a hydrogen
sulfide
removal unit followed in series by a carbon dioxide removal unit. As another
example, a
contaminant removal unit may comprise a first removal unit for a first
contaminant followed
in series by a second removal unit for a second contaminant. As yet another
example, a
compressor may comprise a first compressor to compress a stream to a first
pressure,
followed in series by a second compressor to further compress the stream to a
second (higher)
pressure.
[0072] The term "a portion of the carbonaceous feedstock" refers to carbon
content of
unreacted feedstock as well as partially reacted feedstock, as well as other
components that
may be derived in whole or part from the carbonaceous feedstock (such as
carbon monoxide,
hydrogen and methane). For example, "a portion of the carbonaceous feedstock"
includes
carbon content that may be present in by-product char and recycled fines,
which char is
ultimately derived from the original carbonaceous feedstock.
[0073] The term "superheated steam" in the context of the present invention
refers to a steam
stream that is non-condensing under the conditions utilized.
[0074] The term "syngas demand" refers to the maintenance of syngas balance in
the
hydromethanation reactor for the reaction of step (b). As indicated above, in
the overall
desirable steady-state hydromethanation reaction (see equations (I), (II) and
(III) above),
hydrogen and carbon monoxide are generated and consumed in relative balance.
Because
both hydrogen and carbon monoxide are withdrawn as part of the gaseous
products, hydrogen
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and carbon monoxide must be added to and/or generated in situ in (via a
combustion/oxidation reaction with supplied oxygen as discussed below) the
hydromethanation reactor in an amount at least required to substantially
maintain this
reaction balance. For the purposes of the present invention, the amount of
hydrogen and
carbon monoxide that must be added to and/or generated in situ for the
hydromethanation
reaction (step (b)) is the "syngas demand".
[0075] The term "steam demand" refers to the amount of steam that must be
added to the
hydromethanation reactor. Steam is consumed in the hydromethanation reaction
and some
steam must be added to the hydromethanation reactor. The theoretical
consumption of steam
is two moles for every two moles of carbon in the feed to produce one mole of
methane and
one mole of carbon dioxide (see equation (V)). In actual practice, the steam
consumption is
not perfectly efficient and steam is withdrawn with the product gases;
therefore, a greater
than theoretical amount of steam needs to be added to the hydromethanation
reactor, which
added amount is the "steam demand". Steam can be added, for example, via the
superheated
steam stream and the oxygen-rich gas stream. The amount of steam to be added
(and the
source) is discussed in further detail below. Steam generated in situ from the
carbonaceous
feedstock (e.g., from vaporization of any moisture content of the carbonaceous
feedstock, or
from an oxidation reaction with hydrogen, methane and/or other hydrocarbons
present in or
generated from the carbonaceous feedstock) can assist in satisfying the steam
demand;
however, it should be noted that any steam generated in situ or fed into the
hydromethanation
reactor at a temperature lower than the hydromethanation reaction temperature
will have an
impact on the "heat demand" for the hydromethanation reaction.
[0076] The term "heat demand" refers to the amount of heat energy that must be
added to the
hydromethanation reactor and generated in situ (for example, via the reaction
of step (c)) to
keep the reaction of step (b) in substantial thermal balance, as discussed
above and as further
detailed below.
[0077] Although methods and materials similar or equivalent to those described
herein can
be used in the practice or testing of the present disclosure, suitable methods
and materials are
described herein. The materials, methods, and examples herein are thus
illustrative only and,
except as specifically stated, are not intended to be limiting.
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General Process Information
[0078] In one embodiment of the invention, a methane-enriched raw product gas
stream (50)
is ultimately generated from a non-gaseous carbonaceous material (10) as
illustrated in Figure
1.
[0079] In accordance with an embodiment of the invention, the non-gaseous
carbonaceous
material (10) is processed in a feedstock preparation unit (100) to generate a
carbonaceous
feedstock (32) which is fed to a catalyst application unit (350) where
hydromethanation
catalyst is applied to generate a catalyzed carbonaceous feedstock (31+32).
The
hydromethanation catalyst will typically comprise a recycle catalyst from
recycle catalyst
stream (57) and a makeup catalyst from make-up catalyst stream (56). Further
details are
provided below.
[0080] The catalyzed carbonaceous feedstock (31+32) is fed into a
hydromethanation reactor
(200) along with a superheated steam stream (12), an oxygen-rich gas stream
(14) and,
optionally, a superheated syngas feed stream (16). The superheated steam
stream (12) and
optional superheated syngas feed stream (16) may be a single feed stream which
comprises,
or multiple feed streams which, in combination with the oxygen-rich gas stream
(14) and in
situ generation of heat energy, syngas and steam comprise, steam and heat
energy, and
optionally hydrogen and carbon monoxide, as required to at least substantially
satisfy, or at
least satisfy, the syngas, steam and heat demands of the hydromethanation
reaction that takes
place in hydromethanation reactor (200).
[0081] In one embodiment, as disclosed in commonly owned US Patent Application
Ser. No.
13/211,476 (attorney docket no. FN-0063 US NP1, entitled HYDROMETHANATION OF A
CARBONACEOUS FEEDSTOCK, filed 17 August 2011), the optional superheated syngas
feed
stream (16) is not present, and the catalyzed carbonaceous feedstock (31+32),
superheated
steam stream (12) and oxygen-rich gas stream (14) are all fed to
hydromethanation reactor
(200) at a temperature below the target operating temperature of the
hydromethanation
reaction.
[0082] In accordance with the present invention, the carbonaceous feedstock
(32), such as
catalyzed carbonaceous feedstock (31+32), is substantially free-flowing and
fed to
hydromethanation reactor (200) with an elevated moisture content as discussed
in further
detail below.
[0083] The hydromethanation reactor (200) comprises a fluidized bed (202) with
an upper
portion (202b), and a lower portion (202c), in which the reactions of step (b)
and step (c) take
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place. Without
being bound by any particular theory, the reaction of step (b)
(hydromethanation reaction) predominates in upper portion (202b), and the
reaction of step
(c) (oxidation reaction) predominates in lower portion (202c). It is believed
that there is no
specific defined boundary between the two portions, but rather there is a
transition as oxygen
is consumed (and heat energy and syngas are generated) in lower portion
(202c). It is also
believed that oxygen consumption is rapid under the conditions present in
hydromethanation
reactor (200); therefore, the predominant portion of fluidized bed (202) will
be upper portion
(202b).
[0084] The superheated steam stream (12) and oxygen-rich gas stream (14) may
be fed
separately into the hydromethanation reactor (200), but are typically combined
prior to
feeding into lower portion (202c) of fluidized bed (202). In one embodiment,
the temperature
of both streams (individually and combined) upon introduction to lower section
(202c) of
fluidized bed (202) will be lower than the target operating temperature of the
reaction of step
(b).
[0085] At least a portion of the carbonaceous feedstock in lower portion
(202c) of fluidized
bed (202) will react with oxygen from oxygen-rich gas stream (14) to generate
heat energy,
and also hydrogen and carbon monoxide (syngas), desirably in sufficient
amounts to satisfy
the heat and syngas demands of the hydromethanation reaction of step (b)
(desirably no
separate superheated syngas feed stream (16) is utilized in steady-state
operation of the
process). This includes the reaction of solid carbon from unreacted (fresh)
feedstock,
partially reacted feedstock (such as char and recycled fines), as well gases
(carbon monoxide,
hydrogen, methane and higher hydrocarbons) that may be generated from or
carried with the
feedstock and recycle fines in lower portion (202c). Generally some water
(steam) may be
produced, as well as other by-products such as carbon dioxide depending on the
extent of
combustion/oxidation.
[0086] In hydromethanation reactor (200) (predominantly in upper portion
(202b) of
fluidized bed (202)), the carbonaceous feedstock, steam, hydrogen and carbon
monoxide
react in the presence of the hydromethanation catalyst to generate a methane-
enriched raw
product, which is ultimately withdrawn as a methane-enriched raw product
stream (50) from
the hydromethanation reactor (200).
[0087] The reactions of the carbonaceous feedstock in fluidized bed (202) also
results in a
by-product char comprising unreacted carbon as well as non-carbon content from
the
carbonaceous feedstock (including hydromethanation catalyst) as described in
further detail
below. To prevent buildup of the residue in the hydromethanation reactor
(200), a solid
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purge of by-product char is routinely withdrawn (periodically or continuously)
via char
withdrawal line (58).
[0088] In one embodiment of the present invention, as disclosed in commonly
owned and
previously incorporated U.S. Provisional Application Serial No. / ___ ,
(attorney docket
no. FN-0065 US PRV, entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK,
concurrently filed herewith), carbonaceous feedstock (32) (or catalyzed
carbonaceous
feedstock (31+32)) is also fed into lower portion (202c) of fluidized bed
(202). Because
catalyzed carbonaceous feedstock (31+32) is introduced into lower portion
(202c) of
fluidized bed (202), char withdrawal line (58) will be located at a point such
that by-product
char is withdrawn from fluidized bed (202) at one or more points above the
feed location of
catalyzed carbonaceous feedstock (31+32), typically from upper portion (202b)
of fluidized
bed (202).
[0089] In this embodiment, due to the lower feed point of catalyzed
carbonaceous feedstock
(31+32) into hydromethanation reactor (200), and higher withdrawal point of by-
product char
from hydromethanation reactor (200), hydromethanation reactor (200) with be a
flow-up
configuration as discussed below.
[0090] Hydromethanation reactor (200) also typically comprises a zone (206)
below
fluidized-bed (202), with the two sections typically being separated by a grid
plate (208) or
similar divider. Particles too large to be fluidized in fluidized-bed section
(202), for example
large-particle by-product char and non-fluidizable agglomerates, are generally
collected in
lower portion (202c) of fluidized bed (202), as well as zone (206). Such
particles will
typically comprise a carbon content (as well as an ash and catalyst content),
and may be
removed periodically from hydromethanation reactor (200) via char withdrawal
lines (58)
and (58a) for catalyst recovery as discussed below.
[0091] Typically, the methane-enriched raw product passes through an initial
disengagement
zone (204) above the fluidized-bed section (202) prior to withdrawal from
hydromethanation
reactor (200). The disengagement zone (204) may optionally contain, for
example, one or
more internal cyclones and/or other entrained particle disengagement
mechanisms. The
"withdrawn" (see discussion below) methane-enriched raw product gas stream
(50) typically
comprises at least methane, carbon monoxide, carbon dioxide, hydrogen,
hydrogen sulfide,
steam, heat energy and entrained fines.
[0092] The methane-enriched raw product gas stream (50) is initially treated
to remove a
substantial portion of the entrained fines, typically via a cyclone assembly
(360) (for
example, one or more internal and/or external cyclones), which may be followed
if necessary
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by optional additional treatments such as Venturi scrubbers, as discussed in
more detail
below. The "withdrawn" methane-enriched raw product gas stream (50),
therefore, is to be
considered the raw product prior to fines separation, regardless of whether
the fines
separation takes place internal to and/or external of hydromethanation reactor
(200).
[0093] As specifically depicted in Figure 1, the methane-enriched raw product
stream (50) is
passed from hydromethanation reactor (200) to a cyclone assembly (360) for
entrained
particle separation. While cyclone assembly (360) is shown in Figure 1 as a
single external
cyclone for simplicity, as indicated above cyclone assembly (360) may be an
internal and/or
external cyclone, and may also be a series of multiple internal and/or
external cyclones.
[0094] The methane-enriched raw product gas stream (50) is treated in cyclone
assembly
(360) to generate the fines-depleted methane-enriched raw product gas stream
(52) and a
recovered fines stream (362).
[0095] Recovered fines stream (362) may be fed back into hydromethanation
reactor (202),
for example, into upper portion (202b) of fluidized bed (202) via fines
recycle line (364),
and/or into lower portion (202c) of fluidized bed (202) via fines recycle line
(366) (as
disclosed in commonly owned US Provisional Application Ser. No. 13/228,821
(attorney
docket no. FN-0064 US NP1, entitled HYDROMETHANATION OF A CARBONACEOUS
FEEDSTOCK, filed 9 September 2011)). To the extent not fed back into fluidized
bed (202),
recovered fines stream (362) may, for example, be recycled back to feedstock
preparation
unit (100) and/or catalyst recovery unit (300).
[0096] The fines-depleted methane-enriched raw product gas stream (52)
typically comprises
at least methane, carbon monoxide, carbon dioxide, hydrogen, hydrogen sulfide,
steam,
ammonia and heat energy, as well as small amounts of contaminants such as
remaining
residual entrained fines, and other volatilized and/or carried material (for
example, mercury)
that may be present in the carbonaceous feedstock. There are typically
virtually no (total
typically less than about 50 ppm) condensable (at ambient conditions)
hydrocarbons present
in fines-depleted methane-enriched raw product gas stream (52).
[0097] The fines-depleted methane-enriched raw product gas stream (52) may be
treated in
one or more downstream processing steps to recover heat energy, decontaminate
and convert,
to produce one or more value-added products such as, for example, substitute
natural gas
(pipeline quality), hydrogen, carbon monoxide, syngas, ammonia, methanol,
other syngas-
derived products and electrical power, as disclosed in many of the documents
referenced in
the "Hydromethanation" section below, and as discussed in further detail
below.
[0098] Additional details and embodiments are provided below.
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Hydromethanation
[0099] Catalytic gasification/hydromethanation and/or raw product conversion
processes and
conditions are generally disclosed, for example, in US3828474, US3998607,
US4057512,
US4092125, US4094650, US4204843, US4468231, US4500323, US4541841, US4551155,
US4558027, US4606105, US4617027, US4609456, US5017282, US5055181, US6187465,
US6790430, US6894183, US6955695, US2003/0167961A1 and US2006/0265953A1, as
well as in commonly owned US2007/0000177A1, US2007/0083072A1,
US2007/0277437A1,
US2009/0048476A1, US2009/0090056A1, US2009/0090055A1, US2009/0165383A1,
US2009/0166588A1, US2009/0165379A1, US2009/0170968A1, US2009/0165380A1,
US2009/0165381A1, US2009/0165361A1, US2009/0165382A1, US2009/0169449A1,
US2009/0169448A1, US2009/0165376A1, US2009/0165384A1, US2009/0217582A1,
US2009/0220406A1, US2009/0217590A1, US2009/0217586A1, US2009/0217588A1,
US2009/0218424A1, US2009/0217589A1, US2009/0217575A1, US2009/0229182A1,
US2009/0217587A1, US2009/0246120A1, US2009/0259080A1, US2009/0260287A1,
US2009/0324458A1, US2009/0324459A1, US2009/0324460A1, US2009/0324461A1,
US2009/0324462A1, US2010/0076235A1, US2010/0071262A1, US2010/0121125A1,
US2010/0120926A1, US2010/0179232A1, US2010/0168494A1, US2010/0168495A1,
US2010/0292350A1, US2010/0287836A1, US2010/0287835A1, US2011/0031439A1,
US2011/0062012A1, US2011/0062722A1, US2011/0062721A1, US2011/0064648A1,
US2011/0088896A1, US2011/0088897A1, US2011/0146978A1, US2011/0146979A1,
US2011/0207002A1 and US2011/0217602A1, as well as US Patent Applications
Serial No.
13/094,438 (attorney docket no. FN-0061 US NP1, entitled HYDROMETHANATION OF A
CARBONACEOUS FEEDSTOCK WITH VANADIUM RECOVERY), which was filed 26 April 2011;
US Patent Application Ser. No. 13/211,476 (attorney docket no. FN-0063 US NP1,
entitled
HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, filed 17 August 2011); and US
Patent Application Ser. No. 13/228,821 (attorney docket no. FN-0064 US NP1,
entitled
HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, filed 9 September 2011).
[00100] In an embodiment in accordance with the present invention as
illustrated in Figure 1,
catalyzed carbonaceous feedstock (31+32), superheated steam stream (12) and,
optionally,
superheated syngas feed stream (16) are introduced into hydromethanation
reactor (200). In
addition, an amount of an oxygen-rich gas stream (14) is also be introduced
into
hydromethanation reactor for in situ generation of heat energy and syngas, as
generally
discussed above and disclosed in many of the previously incorporated
references (see, for
16
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example, previously incorporated
US2010/0076235A1, US2010/0287835A 1,
US2011/0062721A1 and US Patent Application Serial No. 13/211,476).
[00101] Superheated steam stream (12), oxygen-rich gas stream (14) and
superheated syngas
feed stream (16) (if present) are desirably introduced into hydromethanation
reactor at a
temperature below the target operating temperature of the hydromethanation
reaction.
Although under those conditions this would have a negative impact on the heat
demand of the
hydromethanation reaction (prior to the reaction of step (c)), this actually
allows full
steam/heat integration of the process, without the use of fuel fired
superheaters (in steady-
state operation of the process) that are typically fueled with a portion of
the product from the
process. Typically, superheated syngas feed stream (16) will not be present.
[00102] Steps (b) and (c) occur within hydromethanation reactor (200).
[00103] Hydromethanation reactor (200) is a fluidized-bed reactor.
Hydromethanation
reactor (200) can, for example, be a "flow down" countercurrent configuration,
where the
catalyzed carbonaceous feedstock (31+32) is introduced at a higher point so
that the particles
flow down the fluidized bed (202) toward lower portion (202c) of fluidized bed
(202), and
the gases flow in an upward direction and are removed at a point above the
fluidized bed
(202).
[00104] Alternatively, hydromethanation reactor (200) has a "flow up" co-
current
configuration, where the catalyzed carbonaceous feedstock (31+32) is fed at a
lower point
(bottom portion (202c) of fluidized bed (202)) so that the particles flow up
the fluidized bed
(202), along with the gases, to a char by-product removal zone, for example,
near or at the
top of upper portion (202b) of fluidized bed (202), to the top of fluidized
bed (202). In one
embodiment, the feed point of the carbonaceous feedstock (such as catalyzed
carbonaceous
feedstock (31+32)) should result in introduction into fluidized bed (200) as
close to the point
of introduction of oxygen (from oxygen-rich gas stream (14)) as reasonably
possible. See,
for example, commonly owned and previously incorporated U.S. Patent
Application Serial
No. / __ , _______________________________________________________
(attorney docket no. FN-0065 US NP1, entitled HYDROMETHANATION OF A
CARBONACEOUS FEEDSTOCK, concurrently filed herewith)
[00105] Hydromethanation reactor (200) is typically operated at moderately
high pressures
and temperatures, requiring introduction of solid streams (e.g., catalyzed
carbonaceous
feedstock (31+32) and if present recycle fines) to the reaction chamber of the
reactor while
maintaining the required temperature, pressure and flow rate of the streams.
Those skilled in
the art are familiar with feed inlets to supply solids into the reaction
chambers having high
pressure and/or temperature environments, including star feeders, screw
feeders, rotary
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pistons and lock-hoppers. It should be understood that the feed inlets can
include two or
more pressure-balanced elements, such as lock hoppers, which would be used
alternately. In
some instances, the carbonaceous feedstock can be prepared at pressure
conditions above the
operating pressure of the reactor and, hence, the particulate composition can
be directly
passed into the reactor without further pressurization. Gas for pressurization
can be an inert
gas such as nitrogen, or more typically a stream of carbon dioxide that can,
for example be
recycled from a carbon dioxide stream generated by an acid gas removal unit.
[00106] Hydromethanation reactor (200) is desirably operated at a moderate
temperature (as
compared to conventional gasification processes), with a target operating
temperature of at
least about 1000 F (about 538 C), or at least about 1100 F (about 593 C), to
about 1500 F
(about 816 C), or to about 1400 F (about 760 C), or to about 1300 F (704 C);
and a pressure
of about 250 psig (about 1825 kPa, absolute), or about 400 psig (about 2860
kPa), or about
450 psig (about 3204 kPa), to about 800 psig (about 5617 kPa), or to about 700
psig (about
4928 kPa), or to about 600 psig (about 4238 kPa), or to about 500 psig (about
3549 kPa),.
[00107] Typical gas flow velocities in hydromethanation reactor (200) are from
about 0.5
ft/sec (about 0.15 m/sec), or from about 1 ft/sec (about 0.3 m/sec), to about
2.0 ft/sec (about
0.6 m/sec), or to about 1.5 ft/sec (about 0.45 m/sec).
[00108] As oxygen-rich gas stream (14) is fed into hydromethanation reactor
(200), a portion
of the carbonaceous feedstock (desirably carbon from the partially reacted
feedstock, by-
product char and recycled fines) will be consumed in an oxidation/combustion
reaction,
generating heat energy as well as typically some amounts carbon monoxide and
hydrogen
(and typically other gases such as carbon dioxide and steam). The variation of
the amount of
oxygen supplied to hydromethanation reactor (200) provides an advantageous
process control
to ultimately maintain syngas and heat balance. Increasing the amount of
oxygen will
increase the oxidation/combustion, and therefore increase in situ heat
generation. Decreasing
the amount of oxygen will conversely decrease the in situ heat generation. The
amount of
syngas generated will ultimately depend on the amount of oxygen utilized, and
higher
amounts of oxygen may result in a more complete combustion/oxidation to carbon
dioxide
and water, as opposed to a more partial combustion to carbon monoxide and
hydrogen.
[00109] The amount of oxygen supplied to hydromethanation reactor (200) must
be
sufficient to combust/oxidize enough of the carbonaceous feedstock to generate
enough heat
energy and syngas to meet the heat and syngas demands of the steady-state
hydromethanation
reaction.
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[00110] In one embodiment, the amount of molecular oxygen (as contained in the
oxygen-
rich gas stream (14)) that is provided to the hydromethanation reactor (200)
can range from
about 0.10, or from about 0.20, or from about 0.25, to about 0.6, or to about
0.5, or to about
0.4, or to about 0.35 pounds of 02 per pound of carbonaceous feedstock.
[00111] The hydromethanation and oxidation/combustion reactions will occur
contemporaneously. Depending on the configuration of hydromethanation reactor
(200), the
two steps predominant in separate zones ¨ the hydromethanation in upper
portion (202b) of
fluidized bed (202), and the oxidation/combustion in lower portion (202c) of
fluidized bed
(202). The oxygen-rich gas stream (14) is typically mixed with superheated
steam stream
(12) and the mixture introduced at or near the bottom of fluidized bed (202)
in lower portion
(202c) to avoid formation of hot spots in the reactor, and to avoid (minimize)
combustion of
the desired gaseous products. In accordance with the present invention,
feeding the catalyzed
carbonaceous feedstock (31+32) with an elevated moisture content, and
particularly into
lower portion (202c) of fluidized bed (202), also assists in heat dissipation
and the avoidance
if formation of hot spots in reactor (200).
[00112] If superheated syngas feed stream (16) is present, that stream will
typically be
introduced as a mixture with steam stream (12), with oxygen-rich gas stream
(14) introduced
separately into lower portion (202c) of fluidized bed (202) so as to not
preferentially consume
the syngas components.
[00113] The oxygen-rich gas stream (14) can be fed into hydromethanation
reactor (200) by
any suitable means such as direct injection of purified oxygen, oxygen-air
mixtures, oxygen-
steam mixtures, or oxygen-inert gas mixtures into the reactor. See, for
instance, US4315753
and Chiaramonte et al., Hydrocarbon Processing, Sept. 1982, pp. 255- 257.
[00114] The oxygen-rich gas stream (14) is typically generated via standard
air-separation
technologies, and will be fed mixed with steam, and introduced at a
temperature above about
250 F (about 121 C), to about 400 F (about 204 C), or to about 350 F (about
177 C), or to
about 300 F (about 149 C), and at a pressure at least slightly higher than
present in
hydromethanation reactor (200). The steam in oxygen-rich gas stream (14)
should be non-
condensable during transport of oxygen-rich stream (14) to hydromethanation
reactor (200),
so oxygen-rich stream (14) may need to be transported at a lower pressure then
pressurized
(compressed) just prior to introduction into hydromethanation reactor (200).
[00115] As indicated above, the hydromethanation reaction has a steam demand,
a heat
demand and a syngas demand. These conditions in combination are important
factors in
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determining the operating conditions for the hydromethanation reaction as well
as the
remainder of the process.
[00116] For example, the steam demand of the hydromethanation reaction
requires a molar
ratio of steam to carbon (in the feedstock) of at least about 1. Typically,
however, the molar
ratio is greater than about 1, or from about 1.5 (or greater), to about 6 (or
less), or to about 5
(or less), or to about 4 (or less), or to about 3 (or less), or to about 2 (or
less). The moisture
content of the catalyzed carbonaceous feedstock (31+32), moisture generated
from the
carbonaceous feedstock in the hydromethanation reactor (200), and steam
included in the
superheated steam stream (12), oxygen-rich gas stream (14) and recycle fines
stream(s) (and
optional superheated syngas feed stream (16)), should be sufficient to at
least substantially
satisfy (or at least satisfy) the steam demand of the hydromethanation
reaction.
[00117] As also indicated above, the hydromethanation reaction (step (b)) is
essentially
thermally balanced but, due to process heat losses and other energy
requirements (for
example, vaporization of moisture on the feedstock), some heat must be
generated in the
hydromethanation reaction to maintain the thermal balance (the heat demand).
The partial
combustion/oxidation of carbon in the presence of the oxygen introduced into
hydromethanation reactor (200) from oxygen-rich gas stream (14) should be
sufficient to at
least substantially satisfy (or at least satisfy) both the heat and syngas
demand of the
hydromethanation reaction.
[00118] The gas utilized in hydromethanation reactor (200) for pressurization
and reaction of
the catalyzed carbonaceous feedstock (31+32) comprises the superheated steam
stream (12)
and oxygen-rich gas stream (14) (and optional superheated syngas feed stream
(16)) and,
optionally, additional nitrogen, air, or inert gases such as argon, which can
be supplied to
hydromethanation reactor (200) according to methods known to those skilled in
the art. As a
consequence, the superheated steam stream (12) and oxygen-rich gas stream (14)
must be
provided at a higher pressure which allows them to enter hydromethanation
reactor (200).
[00119] Desirably, all streams should be fed into hydromethanation reactor
(200) at a
temperature less than the target operating temperature of the hydromethanation
reactor, such
as disclosed in previously incorporated US Provisional Application Ser. No.
13/211,476.
[00120] Superheated steam stream (12) can be at a temperature as low as the
saturation point
at the feed pressure, but it is desirable to feed at a temperature above this
to avoid the
possibility of any condensation occurring. Typical feed temperatures of
superheated steam
stream (12) are from about 500 F (about 260 C), or from about 600 F (about 316
C), or from
about 700 F (about 371 C), to about 950 F (about 510 C), or to about 900 F
(about 482 C).
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The temperature of superheated steam stream (12) will ultimately depend on the
level of heat
recovery from the process, as discussed below. In any event, no fuel fired
superheater should
be used in the superheating of steam stream (12) in steady-state operation of
the process.
[00121] When superheated steam stream (12) and oxygen-rich stream (14) are
combined for
feeding into lower section (202c) of fluidized bed (202), the temperature of
the combined
stream will typically range from about from about 500 F (about 260 C), or from
about 600 F
(about 316 C), or from about 700 F (about 371 C), to about 900 F (about 482
C), or to about
850 F (about 454 C).
[00122] The temperature in hydromethanation reactor (200) can be controlled,
for example,
by controlling the amount and temperature of the superheated steam stream
(12), as well as
the amount of oxygen supplied to hydromethanation reactor (200).
[00123] Advantageously, steam for the hydromethanation reaction is generated
from other
process operations through process heat capture (such as generated in a waste
heat boiler,
generally referred to as "process steam" or "process-generated steam") and, in
some
embodiments, is solely supplied as process-generated steam. For example,
process steam
streams generated by a heat exchanger unit or waste heat boiler can be fed to
hydromethanation reactor (200) as part of superheated steam stream (12), such
as disclosed,
for example, in previously incorporated US2010/0287835A1 and US Patent
Application Ser.
No. 13/211,476, and as discussed below.
[00124] In certain embodiments, the overall process described herein is at
least substantially
steam neutral, such that steam demand (pressure and amount) for the
hydromethanation
reaction can be satisfied via heat exchange with process heat at the different
stages therein, or
steam positive, such that excess steam is produced and can be used, for
example, for power
generation. Desirably, process-generated steam accounts for greater than about
95 wt%, or
greater than about 97 wt%, or greater than about 99 wt%, or about 100 wt% or
greater, of the
steam demand of the hydromethanation reaction.
[00125] The result of the hydromethanation reaction is a methane-enriched raw
product,
which is withdrawn from hydromethanation reactor (200) as methane-enriched raw
product
stream (50) typically comprising CH4, CO2, H2, CO, H25, unreacted steam and,
optionally,
other contaminants such as entrained fines, NH3, COS, HCN and/or elemental
mercury vapor,
depending on the nature of the carbonaceous material utilized for
hydromethanation.
[00126] If the hydromethanation reaction is run in syngas balance, the methane-
enriched raw
product stream (50), upon exiting the hydromethanation reactor (200), will
typically comprise
at least about 15 mol%, or at least about 18 mol%, or at least about 20 mol%,
methane based
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on the moles of methane, carbon dioxide, carbon monoxide and hydrogen in the
methane-
enriched raw product stream (50). In addition, the methane-enriched raw
product stream (50)
will typically comprise at least about 50 mol% methane plus carbon dioxide,
based on the
moles of methane, carbon dioxide, carbon monoxide and hydrogen in the methane-
enriched
raw product stream (50).
[00127] If the hydromethanation reaction is run in syngas excess, e.g.,
contains an excess of
carbon monoxide and/or hydrogen above and beyond the syngas demand (for
example,
excess carbon monoxide and/or hydrogen are generated due to the amount of
oxygen-rich gas
stream (14) fed to hydromethanation reactor (200)), then there may be some
dilution effect on
the molar percent of methane and carbon dioxide in methane-enriched raw
product stream
(50).
[00128] The non-gaseous carbonaceous materials (10) useful in these processes
include, for
example, a wide variety of biomass and non-biomass materials. The carbonaceous
feedstock
(32) is derived from one or more non-gaseous carbonaceous materials (10),
which are
processed in a feedstock preparation section (100) as discussed below.
[00129] The hydromethanation catalyst (31) can comprise one or more catalyst
species, as
discussed below.
[00130] The carbonaceous feedstock (32) and the hydromethanation catalyst (31)
are
typically intimately mixed (i.e., to provide a catalyzed carbonaceous
feedstock (31+32))
before provision to the hydromethanation reactor (200).
Further Gas Processing
Fines Removal
[00131] The hot gas effluent leaving the reaction chamber of the
hydromethanation reactor
(200) can pass through a fines remover unit (such as cyclone assembly (360)),
incorporated
into and/or external of the hydromethanation reactor (200), which serves as a
disengagement
zone. Particles too heavy to be entrained by the gas leaving the
hydromethanation reactor
(200) (i.e., fines) are returned to the hydromethanation reactor (200), for
example, to the
reaction chamber (e.g., fluidized bed (202)).
[00132] Residual entrained fines are substantially removed by any suitable
device such as
internal and/or external cyclone separators optionally followed by Venturi
scrubbers. As
discussed above, at least a portion of these fines are returned to lower
section (202c) of
fluidized bed (202) via recycle line (366). A portion may also be returned to
upper portion
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(202b) of fluidized bed (202) via recycle line (364). Any remaining recovered
fines can be
processed to recover alkali metal catalyst, or directly recycled back to
feedstock preparation
as described in previously incorporated US2009/0217589A1.
[00133] Removal of a "substantial portion" of fines means that an amount of
fines is
removed from the resulting gas stream such that downstream processing is not
adversely
affected; thus, at least a substantial portion of fines should be removed.
Some minor level of
ultrafine material may remain in the resulting gas stream to the extent that
downstream
processing is not significantly adversely affected. Typically, at least about
90 wt%, or at least
about 95 wt%, or at least about 98 wt%, of the fines of a particle size
greater than about 20
um, or greater than about 10 um, or greater than about 5 um, are removed.
Heat Exchange
[00134] Depending on the hydromethanation conditions, the fines-depleted
methane-
enriched raw product stream (52) can be generated having at a temperature
ranging from
about 1000 F (about 538 C) to about 1500 F (about 816 C), and more typically
from about
1100 F (about 593 C) to about 1400 F (about 760 C), a pressure of from about
50 psig
(about 446 kPa) to about 800 psig (about 5617 kPa), more typically from about
400 psig
(about 2860 kPa) to about 600 psig (about 4238 kPa), and a velocity of from
about 0.5 ft/sec
(about 0.15 m/sec) to about 2.0 ft/sec (about 0.61 m/sec), more typically from
about 1.0 ft/sec
(0.30 m/sec) to about 1.5 ft/sec (about 0.46 m/sec).
[00135] The fines-depleted methane-enriched raw product stream (52) can be,
for example,
provided to a heat recovery unit, e.g., first heat exchanger unit (400) as
shown in Figure 2.
First heat exchanger unit (400) removes at least a portion of the heat energy
from the fines-
depleted methane-enriched raw product stream (52) and reduces the temperature
of the fines-
depleted methane-enriched raw product stream (52) to generate a cooled methane-
enriched
raw product stream (70) having a temperature less than the fines-depleted
methane-enriched
raw product stream (52). The heat energy recovered by second heat exchanger
unit (400) can
be used to generate a first process steam stream (40) of which at least a
portion of the first
process steam stream (40) can, for example, be fed back to the
hydromethanation reactor
(200).
[00136] In one embodiment, as depicted in Figure 2, first heat exchanger unit
(400) has both
a steam boiler section (400b) preceded by a superheating section (400a). A
stream of boiler
feed water (39a) can be passed through steam boiler section (400b) to generate
a first process
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steam stream (40), which is then passed through steam superheater (400a) to
generate a
superheated process steam stream (25) of a suitable temperature and pressure
for introduction
into hydromethanation reactor (200). Steam superheater (400a) can also be used
to superheat
other recycle steam streams (for example second process steam stream (43)) to
the extent
required for feeding into the hydromethanation reactor (200).
[00137] The resulting cooled methane-enriched raw product stream (70) will
typically exit
second heat exchanger unit (400) at a temperature ranging from about 450 F
(about 232 C)
to about 1100 F (about 593 C), more typically from about 550 F (about 288 C)
to about
950 F (about 510 C), a pressure of from about 50 psig (about 446 kPa) to about
800 psig
(about 5617 kPa), more typically from about 400 psig (about 2860 kPa) to about
600 psig
(about 4238 kPa), and a velocity of from about 0.5 ft/sec (about 0.15 m/sec)
to about 2.0
ft/sec (about 0.61 m/sec), more typically from about 1.0 ft/sec (0.30 m/sec)
to about 1.5 ft/sec
(about 0.46 m/sec).
Gas Purification
[00138] Product purification may comprise, for example, water-gas shift
processes (700),
dehydration (450) and acid gas removal (800), and optional trace contaminant
removal (500)
and optional ammonia removal and recovery (600).
Trace Contaminant Removal (500)
[00139] As is familiar to those skilled in the art, the contamination levels
of the gas stream,
e.g., cooled methane-enriched raw product stream (70), will depend on the
nature of the
carbonaceous material used for preparing the carbonaceous feedstocks. For
example, certain
coals, such as Illinois #6, can have high sulfur contents, leading to higher
COS
contamination; and other coals, such as Powder River Basin coals, can contain
significant
levels of mercury which can be volatilized in hydromethanation reactor (200).
[00140] COS can be removed from a gas stream, e.g. the cooled methane-enriched
raw
product stream (70), by COS hydrolysis (see, U53966875, U54011066, U54100256,
U54482529 and U54524050), passing the gas stream through particulate limestone
(see,
U54173465), an acidic buffered Cu504 solution (see, U54298584), an
alkanolamine
absorbent such as methyldiethanolamine, triethanolamine, dipropanolamine or
diisopropanolamine, containing tetramethylene sulfone (sulfolane, see,
U53989811); or
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counter-current washing of the cooled second gas stream with refrigerated
liquid CO2 (see,
US4270937 and US4609388).
[00141] HCN can be removed from a gas stream, e.g., the cooled methane-
enriched raw
product stream (70), by reaction with ammonium sulfide or polysulfide to
generate CO2, H2S
and NH3 (see, US4497784, US4505881 and US4508693), or a two stage wash with
formaldehyde followed by ammonium or sodium polysulfide (see, US4572826),
absorbed by
water (see, US4189307), and/or decomposed by passing through alumina supported
hydrolysis catalysts such as Mo03, TiO2 and/or Zr02 (see, US4810475, US5660807
and US
5968465).
[00142] Elemental mercury can be removed from a gas stream, e.g., the cooled
methane-
enriched raw product stream (70), for example, by absorption by carbon
activated with
sulfuric acid (see, US3876393), absorption by carbon impregnated with sulfur
(see,
US4491609), absorption by a H2S-containing amine solvent (see, US4044098),
absorption by
silver or gold impregnated zeolites (see, US4892567), oxidation to Hg0 with
hydrogen
peroxide and methanol (see, US5670122), oxidation with bromine or iodine
containing
compounds in the presence of SO2 (see, US6878358), oxidation with a H, Cl and
0-
containing plasma (see, US6969494), and/or oxidation by a chlorine-containing
oxidizing gas
(e.g., C10, see, US7118720).
[00143] When aqueous solutions are utilized for removal of any or all of COS,
HCN and/or
Hg, the waste water generated in the trace contaminants removal units can be
directed to a
waste water treatment unit (not depicted).
[00144] When present, a trace contaminant removal of a particular trace
contaminant should
remove at least a substantial portion (or substantially all) of that trace
contaminant from the
so-treated gas stream (e.g., cooled methane-enriched raw product stream (70)),
typically to
levels at or lower than the specification limits of the desired product
stream. Typically, a
trace contaminant removal should remove at least 90%, or at least 95%, or at
least 98%, of
COS, HCN and/or mercury from a cooled first gas stream, based on the weight of
the
contaminant in the prior to treatment.
Ammonia Removal and Recovery (600)
[00145] As is familiar to those skilled in the art, gasification of biomass,
certain coals,
certain petroleum cokes and/or utilizing air as an oxygen source for
hydromethanation reactor
(200) can produce significant quantities of ammonia in the product stream.
Optionally, a gas
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stream, e.g. the cooled methane-enriched raw product stream (70), can be
scrubbed by water
in one or more ammonia removal and recovery units (600) to remove and recover
ammonia.
[00146] The ammonia recovery treatment may be performed, for example, on the
cooled
methane-enriched raw product stream (70), directly from heat exchanger (400)
or after
treatment in one or both of (i) one or more of the trace contaminants removal
units (500), and
(ii) one or more sour shift units (700).
[00147] After scrubbing, the gas stream, e.g., the cooled methane-enriched raw
product
stream (70), will typically comprise at least H2S, CO2, CO, H2 and CH4. When
the cooled
methane-enriched raw product stream (70) has previously passed through a sour
shift unit
(700), then, after scrubbing, the gas stream will typically comprise at least
H2S, CO2, H2 and
CH4.
[00148] Ammonia can be recovered from the scrubber water according to methods
known to
those skilled in the art, can typically be recovered as an aqueous solution
(61) (e.g., 20 wt%).
The waste scrubber water can be forwarded to a waste water treatment unit (not
depicted).
[00149] When present, an ammonia removal process should remove at least a
substantial
portion (and substantially all) of the ammonia from the scrubbed stream, e.g.,
the cooled
methane-enriched raw product stream (70). "Substantial" removal in the context
of ammonia
removal means removal of a high enough percentage of the component such that a
desired
end product can be generated. Typically, an ammonia removal process will
remove at least
about 95%, or at least about 97%, of the ammonia content of a scrubbed first
gas stream,
based on the weight of ammonia in the stream prior to treatment.
Water-Gas Shift (700)
[00150] A portion or all of the methane-enriched raw product stream (e.g.,
cooled methane-
enriched raw product stream (70)) is supplied to a water-gas shift reactor,
such as sour shift
reactor (700).
[00151] In sour shift reactor (700), the gases undergo a sour shift reaction
(also known as a
water-gas shift reaction) in the presence of an aqueous medium (such as steam)
to convert at
least a predominant portion (or a substantial portion, or substantially all)
of the CO to CO2
and to increase the fraction of H2. The generation of increased hydrogen
content is utilized,
for example, to optimize hydrogen production, or to otherwise optimize I-12/C0
ratios for
downstream methanation.
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[00152] The water-gas shift treatment may be performed on the cooled methane-
enriched
raw product stream (70) passed directly from heat exchanger (400), or on the
cooled
methane-enriched raw product stream (70) that has passed through a trace
contaminants
removal unit (500) and/or an ammonia removal unit (600).
[00153] A sour shift process is described in detail, for example, in
US7074373. The process
involves adding water, or using water contained in the gas, and reacting the
resulting water-
gas mixture adiabatically over a steam reforming catalyst. Typical steam
reforming catalysts
include one or more Group VIII metals on a heat-resistant support.
[00154] Methods and reactors for performing the sour gas shift reaction on a
CO-containing
gas stream are well known to those of skill in the art. Suitable reaction
conditions and
suitable reactors can vary depending on the amount of CO that must be depleted
from the gas
stream. In some embodiments, the sour gas shift can be performed in a single
stage within a
temperature range from about 100 C, or from about 150 C, or from about 200 C,
to about
250 C, or to about 300 C, or to about 350 C. In these embodiments, the shift
reaction can be
catalyzed by any suitable catalyst known to those of skill in the art. Such
catalysts include,
but are not limited to, Fe203-based catalysts, such as Fe203-Cr203 catalysts,
and other
transition metal-based and transition metal oxide-based catalysts. In other
embodiments, the
sour gas shift can be performed in multiple stages. In one particular
embodiment, the sour
gas shift is performed in two stages. This two-stage process uses a high-
temperature
sequence followed by a low-temperature sequence. The gas temperature for the
high-
temperature shift reaction ranges from about 350 C to about 1050 C. Typical
high-
temperature catalysts include, but are not limited to, iron oxide optionally
combined with
lesser amounts of chromium oxide. The gas temperature for the low-temperature
shift ranges
from about 150 C to about 300 C, or from about 200 C to about 250 C. Low-
temperature
shift catalysts include, but are not limited to, copper oxides that may be
supported on zinc
oxide or alumina. Suitable methods for the sour shift process are described in
previously
incorporated U52009/0246120A1.
[00155] The sour shift reaction is exothermic so it is often carried out with
a heat exchanger,
such as second heat exchanger unit (401), to permit the efficient use of heat
energy. Shift
reactors employing these features are well known to those of skill in the art.
An example of a
suitable shift reactor is illustrated in previously incorporated U57074373,
although other
designs known to those of skill in the art are also effective.
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[00156] Following the sour gas shift procedure, the resulting hydrogen-
enriched raw product
stream (72) generally contains CH4, CO2, Hz, H2S, steam, optionally CO and
optionally
minor amounts of other contaminants.
[00157] As indicated above, the hydrogen-enriched raw product stream (72) can
be provided
to a heat recovery unit, e.g., second heat exchanger unit (401). While second
heat exchanger
unit (401) is depicted in Figure 2 as a separate unit, it can exist as such
and/or be integrated
into the sour shift reactor (700), thus being capable of cooling the sour
shift reactor (700) and
removing at least a portion of the heat energy from the hydrogen-enriched raw
product stream
(72) to reduce the temperature and generate a cooled stream.
[00158] At least a portion of the recovered heat energy can be used to
generate a second
process steam stream from a water/steam source.
[00159] In a specific embodiment as depicted in Figure 2, the hydrogen-
enriched raw
product stream (72), upon exiting sour shift reactor (700), is introduced into
a superheater
(401a) followed by a boiler feed water preheater (401b). Superheater (401a)
can be used, for
example, to superheat a stream (42a) which can be a portion of cooled methane-
enriched raw
product stream (70), to generate a superheated stream (42b) which is then
recombined into
cooled methane-enriched raw product stream (70). Alternatively, all of cooled
methane-
enriched product stream can be preheated in superheater (401a) and
subsequently fed into
sour shift reactor (700) as superheated stream (42b). Boiler feed water
preheater (401b) can
be used, for example, to preheat boiler feed water (46) to generate a
preheated boiler water
feed stream (39) for one or more of first heat exchanger unit (400) and third
heat exchanger
unit (403), as well as other steam generation operations.
[00160] If it is desired to retain some of the carbon monoxide content of the
methane-
enriched raw product stream (50), a gas bypass loop (71) in communication with
the first heat
recovery unit (400) can be provided to allow some of the cooled methane-
enriched raw
product stream (70) exiting the first heat exchanger unit (400) to bypass the
sour shift reactor
(700) and second heat exchanger unit (401) altogether, and be combined with
hydrogen-
enriched raw product stream (72) at some point prior to dehydration unit (450)
and/or acid
gas removal unit (800). This is particularly useful when it is desired to
recover a separate
methane product, as the retained carbon monoxide can be subsequently
methanated as
discussed below.
Dehydration (450)
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[00161] Subsequent to sour shift reactor (700) and second heat exchanger unit
(401), and
prior to acid gas removal unit (800), the hydrogen-enriched raw product stream
(72) is
typically treated to reduce water content in via a knock-out drum or similar
water separation
device (450). A resulting waste water stream (47) (which will be a sour water
stream) can be
sent to a wastewater treatment unit (not depicted) for further processing. The
resulting
dehydrated hydrogen-enriched raw product stream (72a) is sent to acid gas
removal unit
(800) as discussed below.
Acid Gas Removal (800)
[00162] A subsequent acid gas removal unit (800) is used to remove a
substantial portion of
H25 and a substantial portion of CO2 from the dehydrated hydrogen-enriched raw
product
stream (72a) and generate a sweetened gas stream (80).
[00163] Acid gas removal processes typically involve contacting a gas stream
with a solvent
such as monoethanolamine, diethanolamine, methyldiethanolamine,
diisopropylamine,
diglycolamine, a solution of sodium salts of amino acids, methanol, hot
potassium carbonate
or the like to generate CO2 and/or H25 laden absorbers. One method can involve
the use of
Selexol (UOP LLC, Des Plaines, IL USA) or Rectisol (Lurgi AG, Frankfurt am
Main,
Germany) solvent having two trains; each train containing an H25 absorber and
a CO2
absorber.
[00164] One method for removing acid gases is described in previously
incorporated
US2009/0220406A1.
[00165] At least a substantial portion (e.g., substantially all) of the CO2
and/or H25 (and
other remaining trace contaminants) should be removed via the acid gas removal
processes.
"Substantial" removal in the context of acid gas removal means removal of a
high enough
percentage of the component such that a desired end product can be generated.
The actual
amounts of removal may thus vary from component to component. For "pipeline-
quality
natural gas", only trace amounts (at most) of H25 can be present, although
higher (but still
small) amounts of CO2 may be tolerable.
[00166] Typically, at least about 85%, or at least about 90%, or at least
about 92%, of the
CO2 should be removed from the dehydrated hydrogen-enriched raw product stream
(72a).
Typically, at least about 95%, or at least about 98%, or at least about 99.5%,
of the H25,
should be removed from the dehydrated hydrogen-enriched raw product stream
(72a).
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[00167] Losses of desired product (hydrogen and/or methane) in the acid gas
removal step
should be minimized such that the sweetened gas stream (80) comprises at least
a substantial
portion (and substantially all) of the methane and hydrogen from the
dehydrated hydrogen-
enriched raw product stream (72a). Typically, such losses should be about 2
mol% or less, or
about 1.5 mol% or less, or about 1 mol% of less, respectively, of the methane
and hydrogen
from the dehydrated hydrogen-enriched raw product stream (72a).
[00168] The resulting sweetened gas stream (80) will generally comprise CH4,
H2 and
optionally CO (for the downstream methanation), and typically small amounts of
CO2 and
H20.
[00169] Any recovered H2S (78) from the acid gas removal (and other processes
such as sour
water stripping) can be converted to elemental sulfur by any method known to
those skilled
in the art, including the Claus process. Sulfur can be recovered as a molten
liquid.
[00170] Any recovered CO2 (79) from the acid gas removal can be compressed for
transport
in CO2 pipelines, industrial use, and/or sequestration for storage or other
processes such as
enhanced oil recovery.
[00171] The resulting sweetened gas stream (80) may, for example, be utilized
directly as a
medium/high BTU fuel source, or as a feed for a fuel cell such as disclosed in
previously
incorporated US2011/0207002A1 and US2011/0217602A1, or further processed as
described
below.
Hydrogen Separation Unit (850)
[00172] Hydrogen may be separated from the sweetened gas stream (80) according
to
methods known to those skilled in the art, such as cryogenic distillation, the
use of molecular
sieves, gas separation (e.g., ceramic) membranes, and/or pressure swing
adsorption (PSA)
techniques. See, for example, previously incorporated U52009/0259080A1.
[00173] In one embodiment, a PSA device is utilized for hydrogen separation.
PSA
technology for separation of hydrogen from gas mixtures containing methane
(and optionally
carbon monoxide) is in general well-known to those of ordinary skill in the
relevant art as
disclosed, for example, in U563 79645 (and other citations referenced
therein). PSA devices
are generally commercially available, for example, based on technologies
available from Air
Products and Chemicals Inc. (Allentown, PA), UOP LLC (Des Plaines, IL) and
others.
[00174] In another embodiment, a hydrogen membrane separator can be used
followed by a
PSA device.
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[00175] Such separation provides a high-purity hydrogen product stream (85)
and a
hydrogen-depleted sweetened gas stream (82).
[00176] The recovered hydrogen product stream (85) preferably has a purity of
at least about
99 mole%, or at least 99.5 mole%, or at least about 99.9 mole%.
[00177] The hydrogen product stream (85) can be used, for example, as an
energy source
and/or as a reactant. For example, the hydrogen can be used as an energy
source for
hydrogen-based fuel cells, for power and/or steam generation (see 980, 982 and
984 in Fig.
2), and/or for a subsequent hydromethanation process. The hydrogen can also be
used as a
reactant in various hydrogenation processes, such as found in the chemical and
petroleum
refining industries.
[00178] The hydrogen-depleted sweetened gas stream (82) will comprise
substantially
methane, with optional minor amounts of carbon monoxide (depending primarily
on the
extent of the sour shift reaction and bypass), carbon dioxide (depending
primarily on the
effectiveness of the acid gas removal process) and hydrogen (depending
primarily on the
extent and effectiveness of the hydrogen separation technology). The hydrogen-
depleted
sweetened gas stream (82) can be utilized directly, and/or can be further
processed/utilized as
described below.
Methanation (950)
[00179] All or a portion of sweetened gas stream (80) or hydrogen-depleted
sweetened gas
stream (82) may be used directly as a methane product stream (99), or all or a
portion of
those streams may be further processed/purified to produce methane product
stream (99).
[00180] In one embodiment, sweetened gas stream (80) or hydrogen-depleted
sweetened gas
stream (82) is fed to a trim methanator (950) to generate additional methane
from the carbon
monoxide and hydrogen that may be present in those streams, resulting in a
methane-enriched
product stream (97).
[00181] If a hydrogen separation unit (850) is present, a portion of sweetened
gas stream
(80) may bypass hydrogen separation unit (850) via bypass line (86) to adjust
the hydrogen
content of hydrogen-depleted sweetened gas stream (82) to optimize the I-12/C0
ratio for
methanation.
[00182] The methanation reaction can be carried out in any suitable reactor,
e.g., a single-
stage methanation reactor, a series of single-stage methanation reactors or a
multistage
reactor. Methanation reactors include, without limitation, fixed bed, moving
bed or fluidized
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bed reactors. See, for instance, U53958957, U54252771, U53996014 and
U54235044.
Methanation reactors and catalysts are generally commercially available. The
catalyst used
in the methanation, and methanation conditions, are generally known to those
of ordinary
skill in the relevant art, and will depend, for example, on the temperature,
pressure, flow rate
and composition of the incoming gas stream.
[00183] As the methanation reaction is highly exothermic, in various
embodiments the
methane-enriched product gas stream (97) may be, for example, further provided
to a heat
recovery unit, e.g., third heat exchanger unit (403). While third heat
exchanger unit (403) is
depicted as a separate unit, it can exist as such and/or be integrated into
methanator (950),
thus being capable of cooling the methanator unit and removing at least a
portion of the heat
energy from the methane-enriched gas stream to reduce the temperature of the
methane-
enriched gas stream. The recovered heat energy can be utilized to generate a
second process
steam stream (43) from a water and/or steam source (39b). Although not
depicted as such in
Figure 2, third heat exchanger unit (403) may comprise a superheating section
followed by a
boiler section such as previously described for first heat exchanger unit
(400). Because of the
highly exothermic nature of the methanation reaction, second process stream
(43) will
typically not require further superheating, and all or a portion may be
combined with all or a
portion superheated process steam stream (25) for use as superheated steam
stream (12). If
necessary, however, a superheater (990) may be used to superheat superheated
steam stream
(12) to the desired temperature for feeding into hydromethanation reactor
(200).
[00184] Methane-enriched product gas stream (97) can be utilized as methane
product
stream (99) or, it can be further processed, when necessary, to separate and
recover CH4 by
any suitable gas separation method known to those skilled in the art
including, but not limited
to, cryogenic distillation and the use of molecular sieves or gas separation
(e.g., ceramic)
membranes. Additional gas purification methods include, for example, the
generation of
methane hydrate as disclosed in previously incorporated U52009/0260287A1,
U52009/0259080A1 and U52009/0246120A1.
Pipeline-Quality Natural Gas
[00185] The invention provides processes and systems that, in certain
embodiments, are
capable of generating "pipeline-quality natural gas" (or "pipeline-quality
substitute natural
gas") from the hydromethanation of non-gaseous carbonaceous materials. A
"pipeline-quality
natural gas" typically refers to a methane-containing stream that is (1)
within 5 % of the
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heating value of pure methane (whose heating value is 1010 btudt3 under
standard
atmospheric conditions), (2) substantially free of water (typically a dew
point of about -40 C
or less), and (3) substantially free of toxic or corrosive contaminants. In
some embodiments
of the invention, the methane product stream (99) described in the above
processes satisfies
such requirements.
Waste Water Treatment
[00186] Residual contaminants in waste water resulting from any one or more of
the trace
contaminant removal, sour shift, ammonia removal, acid gas removal and/or
catalyst recovery
processes can be removed in a waste water treatment unit to allow recycling of
the recovered
water within the plant and/or disposal of the water from the plant process
according to any
methods known to those skilled in the art. Depending on the feedstock and
reaction
conditions, such residual contaminants can comprise, for example, aromatics,
CO, CO2, H2S,
COS, HCN, ammonia, and mercury. For example, H2S and HCN can be removed by
acidification of the waste water to a pH of about 3, treating the acidic waste
water with an
inert gas in a stripping column, and increasing the pH to about 10 and
treating the waste
water a second time with an inert gas to remove ammonia (see US5236557). H2S
can be
removed by treating the waste water with an oxidant in the presence of
residual coke particles
to convert the H2S to insoluble sulfates which may be removed by flotation or
filtration (see
US4478425). Aromatics can be removed by contacting the waste water with a
carbonaceous
char optionally containing mono- and divalent basic inorganic compounds (e.g.,
the solid
char product or the depleted char after catalyst recovery, supra) and
adjusting the pH (see
US4113615). Aromatics can also be removed by extraction with an organic
solvent followed
by treatment of the waste water in a stripping column (see US3972693,
US4025423 and
US4162902).
Process Steam
[00187] A steam feed loop can be provided for feeding the various process
steam streams
(e.g., 25/40 and 43) generated from heat energy recovery.
[00188] The process steam streams can be generated by contacting a water/steam
source
(such as (39a) and (39b)) with the heat energy recovered from the various
process operations
using one or more heat recovery units, such as first and third heat exchanger
units (400) and
(403).
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[00189] Any suitable heat recovery unit known in the art may be used. For
example, a steam
boiler or any other suitable steam generator (such as a shell/tube heat
exchanger) that can
utilize the recovered heat energy to generate steam can be used. The heat
exchangers may
also function as superheaters for steam streams, such as (400a) in Fig. 2, so
that heat recovery
through one of more stages of the process can be used to superheat the steam
to a desired
temperature and pressure, thus eliminating the need for separate fuel fired
superheaters.
[00190] While any water source can be used to generate steam, the water
commonly used in
known boiler systems is purified and deionized (about 0.3-1.0 uS/cm) so that
corrosive
processes are slowed.
[00191] In one embodiment of the present process, the hydromethanation
reaction will have
a steam demand (temperature, pressure and volume), and the amount of process
steam and
process heat recovery is sufficient to provide at least about 97 wt%, or at
least about 98 wt%,
or at least about 99 wt%, or at least about 100% of this total steam demand.
If needed, the
remaining about 3 wt% or less, or about 2 wt% or less, or about 1 wt% or less,
can be
supplied by a make-up steam stream, which can be fed into the system as (or as
a part of)
steam stream (12). In steady-state operation of the process, the process steam
should be an
amount of a sufficient temperature and pressure to meet the steam demand of
the
hydromethanation reaction.
[00192] If needed, a suitable steam boiler or steam generator can be used to
provide the
make-up steam stream. Such boilers can be powered, for example, through the
use of any
carbonaceous material such as powdered coal, biomass etc., and including but
not limited to
rejected carbonaceous materials from the feedstock preparation operations
(e.g., fines, supra).
In one embodiment, such an additional steam boiler/generator may be present,
but is not used
in steady state operation.
[00193] In another embodiment, the process steam stream or streams supply at
least all of
the total steam demand for the hydromethanation reaction, in which during
steady state
operation there is substantially no make-up steam stream.
[00194] In another embodiment, an excess of process steam is generated. The
excess steam
can be used, for example, for power generation via a steam turbine, and/or
drying the
carbonaceous feedstock in a fluid bed drier to a desired moisture content, as
discussed below.
Power Generation
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[00195] A portion of the methane product stream (99) can be utilized for
combustion (980)
and steam generation (982), as can a portion of any recovered hydrogen (85).
As indicated
above, excess recycle steam may be provided to one or more power generators
(984), such as
a combustion or steam turbine, to produce electricity which may be either
utilized within the
plant or can be sold onto the power grid.
Preparation of Carbonaceous Feedstocks
Carbonaceous materials processing (100)
[00196] Particulate carbonaceous materials, such as biomass and non-biomass,
can be
prepared via crushing and/or grinding, either separately or together,
according to any methods
known in the art, such as impact crushing and wet or dry grinding to yield one
or more
carbonaceous particulates. Depending on the method utilized for crushing
and/or grinding of
the carbonaceous material sources, the resulting carbonaceous particulates may
be sized (i.e.,
separated according to size) to provide the carbonaceous feedstock (32) for
use in catalyst
loading processes (350) to form a catalyzed carbonaceous feedstock (31 + 32)
for the
hydromethanation reactor (200).
[00197] Any method known to those skilled in the art can be used to size the
particulates.
For example, sizing can be performed by screening or passing the particulates
through a
screen or number of screens. Screening equipment can include grizzlies, bar
screens, and
wire mesh screens. Screens can be static or incorporate mechanisms to shake or
vibrate the
screen. Alternatively, classification can be used to separate the carbonaceous
particulates.
Classification equipment can include ore sorters, gas cyclones, hydrocyclones,
rake
classifiers, rotating trommels or fluidized classifiers. The carbonaceous
materials can be also
sized or classified prior to grinding and/or crushing.
[00198] The carbonaceous particulate can be supplied as a fine particulate
having an average
particle size of from about 25 microns, or from about 45 microns, up to about
2500 microns,
or up to about 500 microns. One skilled in the art can readily determine the
appropriate
particle size for the carbonaceous particulates. For example, when a fluidized
bed reactor is
used, such carbonaceous particulates can have an average particle size which
enables
incipient fluidization of the carbonaceous materials at the gas velocity used
in the fluidized
bed reactor. Desirable particle size ranges for the hydromethanation reactor
(200) are in the
Geldart A and Geldart B ranges (including overlap between the two), depending
on
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fluidization conditions, typically with limited amounts of fine (below about
25 microns) and
coarse (greater than about 250 microns) material.
[00199] Additionally, certain carbonaceous materials, for example, corn stover
and
switchgrass, and industrial wastes, such as saw dust, either may not be
amenable to crushing
or grinding operations, or may not be suitable for use as such, for example
due to ultra fine
particle sizes. Such materials may be formed into pellets or briquettes of a
suitable size for
crushing or for direct use in, for example, a fluidized bed reactor.
Generally, pellets can be
prepared by compaction of one or more carbonaceous material; see for example,
previously
incorporated U52009/0218424A1. In other examples, a biomass material and a
coal can be
formed into briquettes as described in U54249471, US4152119 and U54225457.
Such
pellets or briquettes can be used interchangeably with the preceding
carbonaceous
particulates in the following discussions.
[00200] Additional feedstock processing steps may be necessary depending on
the qualities
of carbonaceous material sources. Biomass may contain high moisture contents,
such as
green plants and grasses, and may require drying prior to crushing. Municipal
wastes and
sewages also may contain high moisture contents which may be reduced, for
example, by use
of a press or roll mill (e.g., U54436028). Likewise, non-biomass, such as high-
moisture coal,
can require drying prior to crushing. Some caking coals can require partial
oxidation to
simplify operation. Non-biomass feedstocks deficient in ion-exchange sites,
such as
anthracites or petroleum cokes, can be pre-treated to create additional ion-
exchange sites to
facilitate catalyst loading and/or association. Such pre-treatments can be
accomplished by
any method known to the art that creates ion-exchange capable sites and/or
enhances the
porosity of the feedstock (see, for example, previously incorporated US4468231
and
GB1599932). Oxidative pre-treatment can be accomplished using any oxidant
known to the
art.
[00201] The ratio and types of the carbonaceous materials in the carbonaceous
particulates
can be selected based on technical considerations, processing economics,
availability, and
proximity of the non-biomass and biomass sources. The availability and
proximity of the
sources for the carbonaceous materials can affect the price of the feeds, and
thus the overall
production costs of the catalytic gasification process. For example, the
biomass and the non-
biomass materials can be blended in at about 5:95, about 10:90, about 15:85,
about 20:80,
about 25:75, about 30:70, about 35:65, about 40:60, about 45:55, about 50:50,
about 55:45,
about 60:40, about 65:35, about 70:20, about 75:25, about 80:20, about 85:15,
about 90:10, or
about 95:5 by weight on a wet or dry basis, depending on the processing
conditions.
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[00202] Significantly, the carbonaceous material sources, as well as the ratio
of the
individual components of the carbonaceous particulates, for example, a biomass
particulate
and a non-biomass particulate, can be used to control other material
characteristics of the
carbonaceous particulates. Non-biomass materials, such as coals, and certain
biomass
materials, such as rice hulls, typically include significant quantities of
inorganic matter
including calcium, alumina and silica which form inorganic oxides (i.e., ash)
in the catalytic
gasifier. At temperatures above about 500 C to about 600 C, potassium and
other alkali
metals can react with the alumina and silica in ash to form insoluble alkali
aluminosilicates.
In this form, the alkali metal is substantially water-insoluble and inactive
as a catalyst. To
prevent buildup of the residue in the hydromethanation reactor (200), a solid
purge of by-
product char (58) (and (58a)) comprising ash, unreacted carbonaceous material,
and various
other compounds (such as alkali metal compounds, both water soluble and water
insoluble) is
routinely withdrawn.
[00203] In preparing the carbonaceous particulates, the ash content of the
various
carbonaceous materials can be selected to be, for example, about 20 wt% or
less, or about 15
wt% or less, or about 10 wt% or less, or about 5 wt% or less, depending on,
for example, the
ratio of the various carbonaceous materials and/or the starting ash in the
various
carbonaceous materials. In other embodiments, the resulting the carbonaceous
particulates
can comprise an ash content ranging from about 5 wt%, or from about 10 wt%, to
about 20
wt%, or to about 15 wt%, based on the weight of the carbonaceous particulate.
In other
embodiments, the ash content of the carbonaceous particulate can comprise less
than about 20
wt%, or less than about 15 wt%, or less than about 10 wt%, or less than about
8 wt%, or less
than about 6 wt% alumina, based on the weight of the ash. In certain
embodiments, the
carbonaceous particulates can comprise an ash content of less than about 20
wt%, based on
the weight of processed feedstock where the ash content of the carbonaceous
particulate
comprises less than about 20 wt% alumina, or less than about 15 wt% alumina,
based on the
weight of the ash.
[00204] Such lower alumina values in the carbonaceous particulates allow for,
ultimately,
decreased losses of catalysts, and particularly alkali metal catalysts, in the
hydromethanation
portion of the process. As indicated above, alumina can react with alkali
source to yield an
insoluble char comprising, for example, an alkali aluminate or
aluminosilicate. Such
insoluble char can lead to decreased catalyst recovery (i.e., increased
catalyst loss), and thus,
require additional costs of make-up catalyst in the overall process.
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[00205] Additionally, the resulting carbonaceous particulates can have a
significantly higher
% carbon, and thus btu/lb value and methane product per unit weight of the
carbonaceous
particulate. In certain embodiments, the resulting carbonaceous particulates
can have a
carbon content ranging from about 75 wt%, or from about 80 wt%, or from about
85 wt%, or
from about 90 wt%, up to about 95 wt%, based on the combined weight of the non-
biomass
and biomass.
[00206] In one example, a non-biomass and/or biomass is wet ground and sized
(e.g., to a
particle size distribution of from about 25 to about 2500 nm) and then drained
of its free
water (i.e., dewatered) to a wet cake consistency. Examples of suitable
methods for the wet
grinding, sizing, and dewatering are known to those skilled in the art; for
example, see
previously incorporated US2009/0048476A1. The filter cakes of the non-biomass
and/or
biomass particulates formed by the wet grinding in accordance with one
embodiment of the
present disclosure can have a moisture content ranging from about 40% to about
60%, or
from about 40% to about 55%, or below 50%. It will be appreciated by one of
ordinary skill
in the art that the moisture content of dewatered wet ground carbonaceous
materials depends
on the particular type of carbonaceous materials, the particle size
distribution, and the
particular dewatering equipment used. Such filter cakes can be thermally
treated, as
described herein, to produce one or more reduced moisture carbonaceous
particulates.
[00207] Each of the one or more carbonaceous particulates can have a unique
composition,
as described above. For example, two carbonaceous particulates can be
utilized, where a first
carbonaceous particulate comprises one or more biomass materials and the
second
carbonaceous particulate comprises one or more non-biomass materials.
Alternatively, a
single carbonaceous particulate comprising one or more carbonaceous materials
utilized.
Catalyst Loading for Hydromethanation (350)
[00208] The hydromethanation catalyst is potentially active for catalyzing at
least reactions
(I), (II) and (III) described above. Such catalysts are in a general sense
well known to those
of ordinary skill in the relevant art and may include, for example, alkali
metals, alkaline earth
metals and transition metals, and compounds and complexes thereof Typically,
the
hydromethanation catalyst comprises at least an alkali metal, such as
disclosed in many of the
previously incorporated references.
[00209] For the hydromethanation reaction, the one or more carbonaceous
particulates are
typically further processed to associate at least one hydromethanation
catalyst, typically
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comprising a source of at least one alkali metal, to generate a catalyzed
carbonaceous
feedstock (31+32). If a liquid carbonaceous material is used, the
hydromethanation catalyst
may for example be intimately mixed into the liquid carbonaceous material.
[00210] The carbonaceous particulate provided for catalyst loading can be
either treated to
form a catalyzed carbonaceous feedstock (31+32) which is passed to the
hydromethanation
reactor (200), or split into one or more processing streams, where at least
one of the
processing streams is associated with a hydromethanation catalyst to form at
least one
catalyst-treated feedstock stream. The remaining processing streams can be,
for example,
treated to associate a second component therewith. Additionally, the catalyst-
treated
feedstock stream can be treated a second time to associate a second component
therewith.
The second component can be, for example, a second hydromethanation catalyst,
a co-
catalyst, or other additive.
[00211] In one example, the primary hydromethanation catalyst (alkali metal
compound) can
be provided to the single carbonaceous particulate (e.g., a potassium and/or
sodium source),
followed by a separate treatment to provide one or more co-catalysts and
additives (e.g., a
calcium source) to the same single carbonaceous particulate to yield the
catalyzed
carbonaceous feedstock (31+32). For
example, see previously incorporated
US2009/0217590A1 and US2009/0217586A1.
[00212] The hydromethanation catalyst and second component can also be
provided as a
mixture in a single treatment to the single second carbonaceous particulate to
yield the
catalyzed carbonaceous feedstock (31+32).
[00213] When one or more carbonaceous particulates are provided for catalyst
loading, then
at least one of the carbonaceous particulates is associated with a
hydromethanation catalyst to
form at least one catalyst-treated feedstock stream. Further, any of the
carbonaceous
particulates can be split into one or more processing streams as detailed
above for association
of a second or further component therewith. The resulting streams can be
blended in any
combination to provide the catalyzed carbonaceous feedstock (31+32), provided
at least one
catalyst-treated feedstock stream is utilized to form the catalyzed feedstock
stream.
[00214] In one embodiment, at least one carbonaceous particulate is associated
with a
hydromethanation catalyst and optionally, a second component. In another
embodiment,
each carbonaceous particulate is associated with a hydromethanation catalyst
and optionally,
a second component.
[00215] Any methods known to those skilled in the art can be used to associate
one or more
hydromethanation catalysts with any of the carbonaceous particulates and/or
processing
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streams. Such methods include but are not limited to, admixing with a solid
catalyst source
and impregnating the catalyst onto the processed carbonaceous material.
Several
impregnation methods known to those skilled in the art can be employed to
incorporate the
hydromethanation catalysts. These methods include but are not limited to,
incipient wetness
impregnation, evaporative impregnation, vacuum impregnation, dip impregnation,
ion
exchanging, and combinations of these methods.
[00216] In one embodiment, an alkali metal hydromethanation catalyst can be
impregnated
into one or more of the carbonaceous particulates and/or processing streams by
slurrying with
a solution (e.g., aqueous) of the catalyst in a loading tank. When slurried
with a solution of
the catalyst and/or co-catalyst, the resulting slurry can be dewatered to
provide a catalyst-
treated feedstock stream, again typically, as a wet cake. The catalyst
solution can be prepared
from any catalyst source in the present processes, including fresh or make-up
catalyst and
recycled catalyst or catalyst solution. Methods for dewatering the slurry to
provide a wet
cake of the catalyst-treated feedstock stream include filtration (gravity or
vacuum),
centrifugation, and a fluid press.
[00217] In another embodiment, as disclosed in
previously incorporated
U52010/0168495A1, the carbonaceous particulates are combined with an aqueous
catalyst
solution to generate a substantially non-draining wet cake, then mixed under
elevated
temperature conditions and finally dried to an appropriate moisture level.
[00218] One particular method suitable for combining a coal particulate and/or
a processing
stream comprising coal with a hydromethanation catalyst to provide a catalyst-
treated
feedstock stream is via ion exchange as described in previously incorporated
U52009/0048476A1 and U52010/0168494A1. Catalyst loading by ion exchange
mechanism
can be maximized based on adsorption isotherms specifically developed for the
coal, as
discussed in the incorporated reference. Such loading provides a catalyst-
treated feedstock
stream as a wet cake. Additional catalyst retained on the ion-exchanged
particulate wet cake,
including inside the pores, can be controlled so that the total catalyst
target value can be
obtained in a controlled manner. The total amount of catalyst loaded can be
controlled by
controlling the concentration of catalyst components in the solution, as well
as the contact
time, temperature and method, as disclosed in the aforementioned incorporated
references,
and as can otherwise be readily determined by those of ordinary skill in the
relevant art based
on the characteristics of the starting coal.
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[00219] In another example, one of the carbonaceous particulates and/or
processing streams
can be treated with the hydromethanation catalyst and a second processing
stream can be
treated with a second component (see previously incorporated
US2007/0000177A1).
[00220] The carbonaceous particulates, processing streams, and/or catalyst-
treated feedstock
streams resulting from the preceding can be blended in any combination to
provide the
catalyzed second carbonaceous feedstock, provided at least one catalyst-
treated feedstock
stream is utilized to form the catalyzed carbonaceous feedstock (31+32).
Ultimately, the
catalyzed carbonaceous feedstock (31+32) is passed onto the hydromethanation
reactor(s)
(200).
[00221] Generally, each catalyst loading unit comprises at least one loading
tank to contact
one or more of the carbonaceous particulates and/or processing streams with a
solution
comprising at least one hydromethanation catalyst, to form one or more
catalyst-treated
feedstock streams. Alternatively, the catalytic component may be blended as a
solid
particulate into one or more carbonaceous particulates and/or processing
streams to form one
or more catalyst-treated feedstock streams.
[00222] Typically, when the hydromethanation catalyst is solely or
substantially an alkali
metal, it is present in the catalyzed carbonaceous feedstock in an amount
sufficient to provide
a ratio of alkali metal atoms to carbon atoms in the catalyzed carbonaceous
feedstock ranging
from about 0.01, or from about 0.02, or from about 0.03, or from about 0.04,
to about 0.10, or
to about 0.08, or to about 0.07, or to about 0.06.
[00223] With some feedstocks, the alkali metal component may also be provided
within the
catalyzed carbonaceous feedstock to achieve an alkali metal content of from
about 3 to about
times more than the combined ash content of the carbonaceous material in the
catalyzed
carbonaceous feedstock, on a mass basis.
[00224] Suitable alkali metals are lithium, sodium, potassium, rubidium,
cesium, and
mixtures thereof Particularly useful are potassium sources. Suitable alkali
metal compounds
include alkali metal carbonates, bicarbonates, formates, oxalates, amides,
hydroxides,
acetates, or similar compounds. For example, the catalyst can comprise one or
more of
sodium carbonate, potassium carbonate, rubidium carbonate, lithium carbonate,
cesium
carbonate, sodium hydroxide, potassium hydroxide, rubidium hydroxide or cesium
hydroxide, and particularly, potassium carbonate and/or potassium hydroxide.
[00225] Optional co-catalysts or other catalyst additives may be utilized,
such as those
disclosed in the previously incorporated references.
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[00226] The one or more catalyst-treated feedstock streams that are combined
to form the
catalyzed carbonaceous feedstock typically comprise greater than about 50%,
greater than
about 70%, or greater than about 85%, or greater than about 90% of the total
amount of the
loaded catalyst associated with the catalyzed carbonaceous feedstock (31+32).
The
percentage of total loaded catalyst that is associated with the various
catalyst-treated
feedstock streams can be determined according to methods known to those
skilled in the art.
[00227] Separate carbonaceous particulates, catalyst-treated feedstock
streams, and
processing streams can be blended appropriately to control, for example, the
total catalyst
loading or other qualities of the catalyzed carbonaceous feedstock (31+32), as
discussed
previously. The appropriate ratios of the various stream that are combined
will depend on the
qualities of the carbonaceous materials comprising each as well as the desired
properties of
the catalyzed carbonaceous feedstock (31+32). For example, a biomass
particulate stream
and a catalyzed non-biomass particulate stream can be combined in such a ratio
to yield a
catalyzed carbonaceous feedstock (31+32) having a predetermined ash content,
as discussed
previously.
[00228] Any of the preceding catalyst-treated feedstock streams, processing
streams, and
processed feedstock streams, as one or more dry particulates and/or one or
more wet cakes,
can be combined by any methods known to those skilled in the art including,
but not limited
to, kneading, and vertical or horizontal mixers, for example, single or twin
screw, ribbon, or
drum mixers. The resulting catalyzed carbonaceous feedstock (31+32) can be
stored for
future use or transferred to one or more feed operations for introduction into
the
hydromethanation reactor(s). The catalyzed carbonaceous feedstock can be
conveyed to
storage or feed operations according to any methods known to those skilled in
the art, for
example, a screw conveyer or pneumatic transport.
[00229] In accordance with the present invention, the carbonaceous feedstock
as fed to the
hydromethanation reactor contains an elevated moisture content of from greater
than 10 wt%,
or about 12 wt% or greater, or about 15 wt% or greater, to about 25 wt% or
less, or to about
20 wt% or less (based on the total weight of the carbonaceous feedstock), to
the extent that
the carbonaceous feedstock is substantially free-flowing.
[00230] The term "substantially free-flowing" as used herein means the
carbonaceous
feedstock particulates do not agglomerate under feed conditions due to
moisture content.
Desirably, the moisture content of the carbonaceous feedstock particulates is
substantially
internally contained so that there is minimal (or no) surface moisture.
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[00231] A suitable substantially free-flowing catalyzed carbonaceous feedstock
(31+32) can
be produced in accordance with the disclosures of previously incorporated
US2010/0168494A1 and US2010/0168495A1, where the thermal treatment step (after
catalyst application) referred to in those disclosures can be minimized (or
even potentially
eliminated).
[00232] To the extent necessary, excess moisture can be removed from the
catalyzed
carbonaceous feedstock (31+32). For example, the catalyzed carbonaceous
feedstock
(31+32) may be dried with a fluid bed slurry drier (i.e., treatment with
superheated steam to
vaporize the liquid), or the solution thermally evaporated or removed under a
vacuum, or
under a flow of an inert gas, to provide a catalyzed carbonaceous feedstock
having a the
required residual moisture content.
Catalyst Recovery (300)
[00233] Reaction of the catalyzed carbonaceous feedstock (31+32) under the
described
conditions generally provides the fines-depleted methane-enriched raw product
stream (52)
and a solid char by-product (58) (and (58a)) from the hydromethanation reactor
(200). The
solid char by-product (58) typically comprises quantities of unreacted carbon,
inorganic ash
and entrained catalyst. The solid char by-product (58) can be removed from the
hydromethanation reactor (200) for sampling, purging, and/or catalyst recovery
via a char
outlet.
[00234] The term "entrained catalyst" as used herein means chemical compounds
comprising the catalytically active portion of the hydromethanation catalyst,
e.g., alkali metal
compounds present in the char by-product. For example, "entrained catalyst"
can include,
but is not limited to, soluble alkali metal compounds (such as alkali metal
carbonates, alkali
metal hydroxides and alkali metal oxides) and/or insoluble alkali compounds
(such as alkali
metal aluminosilicates). The nature of catalyst components associated with the
char extracted
are discussed, for example, in previously incorporated US2007/0277437A1,
US2009/0165383A1, US2009/0165382A1, US2009/0169449A1 and US2009/0169448A1.
[00235] The solid char by-product is continuously or periodically withdrawn
from the
hydromethanation reactor (200) through a char outlet which can, for example,
be a lock
hopper system, although other methods are known to those skilled in the art.
Methods for
removing solid char product are well known to those skilled in the art. One
such method
taught by EP-A-0102828, for example, can be employed.
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[00236] The char by-product (58) from the hydromethanation reactor (200) may
be passed to
a catalytic recovery unit (300), as described below. Such char by-product (58)
may also be
split into multiple streams, one of which may be passed to a catalyst recovery
unit (300), and
another stream which may be used, for example, as a methanation catalyst (as
described in
previously incorporated U52010/0121125A1) and not treated for catalyst
recovery.
[00237] In certain embodiments, when the hydromethanation catalyst is an
alkali metal, the
alkali metal in the solid char by-product (58) can be recovered to produce a
catalyst recycle
stream (57), and any unrecovered catalyst can be compensated by a catalyst
make-up stream
(57) (see, for example, previously incorporated U52009/0165384A1). The more
alumina
plus silica that is in the feedstock, the more costly it is to obtain a higher
alkali metal
recovery.
[00238] In one embodiment, the solid char by-product (58) from the
hydromethanation
reactor (200) can be quenched with a recycle gas and water to extract a
portion of the
entrained catalyst. The recovered catalyst (57) can be directed to the
catalyst loading unit
(350) for reuse of the alkali metal catalyst. The depleted char (59) can, for
example, be
directed to any one or more of the feedstock preparation operations (100) for
reuse in
preparation of the catalyzed feedstock (via line (59a)), combusted to power
one or more
steam generators (such as disclosed in previously incorporated
U52009/0165376A1)), or
used as such in a variety of applications, for example, as an absorbent (such
as disclosed in
previously incorporated U52009/0217582A1).
[00239] Other particularly useful recovery and recycling processes are
described in
U54459138, as well as previously incorporated U52007/0277437A1
U52009/0165383A1,
U52009/0165382A1, U52009/0169449A1 and U52009/0169448A1. Reference can be had
to those documents for further process details.
[00240] The recycle of catalyst can be to one or a combination of catalyst
loading processes.
For example, all of the recycled catalyst can be supplied to one catalyst
loading process,
while another process utilizes only makeup catalyst. The levels of recycled
versus makeup
catalyst can also be controlled on an individual basis among catalyst loading
processes.
[00241] The by-product char (58) can also be treated for recovery of other by-
products, such
as vanadium, in addition to catalyst recovery, as disclosed in previously
incorporated US
Patent Application Ser. No. 13/094,438.
Multi-Train Processes
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[00242] In the processes of the invention, each process may be performed in
one or more
processing units. For example, one or more hydromethanation reactors may be
supplied with
the carbonaceous feedstock from one or more catalyst loading and/or feedstock
preparation
unit operations. Similarly, the methane-enriched raw product streams generated
by one or
more hydromethanation reactors may be processed or purified separately or via
their
combination at various downstream points depending on the particular system
configuration,
as discussed, for example, in previously incorporated U52009/0324458A1,
U52009/0324459A1, U52009/03 244601, U52009/0324461A1 and U52009/0324462A1.
[00243] In certain embodiments, the processes utilize two or more
hydromethanation
reactors (e.g., 2 ¨ 4 hydromethanation reactors). In such embodiments, the
processes may
contain divergent processing units (i.e., less than the total number of
hydromethanation
reactors) prior to the hydromethanation reactors for ultimately providing the
catalyzed
carbonaceous feedstock to the plurality of hydromethanation reactors, and/or
convergent
processing units (i.e., less than the total number of hydromethanation
reactors) following the
hydromethanation reactors for processing the plurality of methane-enriched raw
product
streams generated by the plurality of hydromethanation reactors.
[00244] When the systems contain convergent processing units, each of the
convergent
processing units can be selected to have a capacity to accept greater than a
1/n portion of the
total feed stream to the convergent processing units, where n is the number of
convergent
processing units. Similarly, when the systems contain divergent processing
units, each of the
divergent processing units can be selected to have a capacity to accept
greater than a 1/m
portion of the total feed stream supplying the convergent processing units,
where m is the
number of divergent processing units.
Examples of Specific Embodiments
[00245] A specific embodiment of the process is one in which the process is a
continuous
process, in which steps (a), (b) and (c), are operated in a continuous manner.
[00246] Another specific embodiment is on in which the superheated steam
stream and
oxygen-rich stream are mixed at or prior to introduction into the lower
portion of the
fluidized bed.
[00247] Another specific embodiment is one in which oxygen-rich gas stream
(14) is
supplied continuously to hydromethanation reactor (200), and the amount of
oxygen provided
is varied as a process control, for example, to control of the desired
operating temperature of
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the hydromethanation reaction. As oxygen is supplied to the hydromethanation
reactor, the
resulting oxidation/combustion reaction (for example with carbon in the by-
product char and
fines) generates heat energy (as well as typically some amounts of carbon
monoxide and
hydrogen). The amount of oxygen supplied to the hydromethanation reactor can
be increased
or decreased to increase or decrease the combustion/oxidation and,
consequently, the amount
of heat energy being generated, in situ in the hydromethanation reactor.
[00248] Another specific embodiment is one where the methane-enriched raw
product
stream is introduced into a first heat exchanger unit to recover heat energy
and generate a
cooled methane-enriched raw product stream.
[00249] Another specific embodiment is one where the heat energy recovered in
the first
heat exchanger unit is used to generate a first process steam stream, and
superheat the first
process steam stream for use as all or a part of the superheated steam stream
for introduction
into the hydromethanation reactor.
[00250] Another specific embodiment is one where at least a portion of the
carbon monoxide
in the cooled methane-enriched raw product stream is steam shifted to generate
heat energy
and a hydrogen-enriched raw product stream.
[00251] Another specific embodiment is one where heat energy is recovered from
the steam
shifting, and at least a portion of the recovered heat energy is utilized to
preheat boiler feed
water for use in generating process steam.
[00252] Another specific embodiment is one where the hydrogen-enriched raw
product
stream is substantially dehydrated to generate a dehydrated hydrogen-enriched
raw product
stream.
[00253] Another specific embodiment is one where a substantial portion of the
carbon
dioxide and a substantial portion of the hydrogen sulfide are removed from the
dehydrated
hydrogen-enriched raw product stream to produce a sweetened gas stream
comprising a
substantial portion of the hydrogen, carbon monoxide (if present in the
dehydrated hydrogen-
enriched raw product stream) and methane from the dehydrated hydrogen-enriched
raw
product stream.
[00254] Another specific embodiment is one where a portion of hydrogen from
the
sweetened gas stream is separated to produce a hydrogen product stream and a
hydrogen-
depleted sweetened gas stream comprising methane, hydrogen and optionally
carbon
monoxide.
[00255] Another specific embodiment is one where carbon monoxide and hydrogen
present
in the sweetened gas stream (or hydrogen-depleted sweetened gas stream, if
present) are
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reacted in a catalytic methanator in the presence of a methanation catalyst to
produce heat
energy and a methane-enriched sweetened gas stream.
[00256] Another specific embodiment is one where heat energy from the
catalytic
methanation is recovered and at least a portion of the recovered heat energy
is utilized to
generate and superheat a second process steam stream.
[00257] Another specific embodiment is one where the superheated steam stream
substantially comprises (or alternatively only comprises) steam from the first
process steam
stream and the second process steam stream.
[00258] Another specific embodiment is one where the process is steam neutral
or steam
positive.
[00259] Another specific embodiment is one in which there is no fuel-fired
superheater is
used to superheat the steam fed to the hydromethanation reactor during steady-
state operation
of the process, which steam is superheated only through process heat recovery.
[00260] Another specific embodiment is one where the methane-enriched
sweetened gas
stream is recovered as a methane product stream.
[00261] Another specific embodiment is one where the methane product stream is
a pipeline-
quality natural gas.
[00262] Another specific embodiment is one where the target operating
temperature of the
hydromethanation reaction (step (b)) is at least about at least about 1000 F
(about 538 C) to
about 1500 F (about 816 C), as described above.
[00263] Another specific embodiment is one where the superheated steam stream
is fed to
the hydromethanation reactor at a temperature of from about 500 F (about 260
C) to about
950 F (about 510 C), as described above.
[00264] Another specific embodiment is one where the superheated steam stream
and the
oxygen-rich stream are combined for feeding into the lower section of the
fluidized bed of the
hydromethanation reactor, and the temperature of the combined stream is from
about from
about 500 F (about 260 C) to about 900 F (about 482 C), as described above.
[00265] Another specific embodiment is one where the syngas demand is
substantially
satisfied (or satisfied) by in situ generation of syngas (step (c));
therefore, substantially no (or
no) syngas is added to the hydromethanation reactor (except as may inherently
be present in
the carbonaceous feedstock or the fines stream fed back into the
hydromethanation reactor).
[00266] Another specific embodiment is one where the steam demand is
substantially
satisfied (or satisfied) by steam in the superheated steam stream, the oxygen-
rich gas stream
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and the fines stream that is recycled back to the hydromethanation reactor, as
well as steam
generated in situ from the carbonaceous feedstock.
[00267] Another specific embodiment is one where the heat demand is
substantially satisfied
(or satisfied) by in situ heat generation (step (c)), as all of the primary
streams provided to the
hydromethanation reactor (the steam stream, the oxygen-rich gas stream the
carbonaceous
feedstock/hydromethanation catalyst and fines recycle stream) are introduced
at a
temperature below the target operating temperature of the hydromethanation
reactor.
[00268] Another specific embodiment is one where the carbonaceous feedstock is
supplied
to the hydromethanation at a feed location, a char by-product is generated by
the reactions of
steps (b) and (c), and char by-product is continuously or periodically
withdrawn from the
hydromethanation reactor at a withdrawal point above the feed point of the
carbonaceous
feedstock. In another embodiment, char by-product is periodically or
continuously
withdrawn from the upper portion of the fluidized bed.
[00269] Another specific embodiment is one where and at least a portion of the
withdrawn
by-product char is provided to a catalyst recovery operation. Recovered
catalyst is then
recycled and combined with makeup catalyst to meet the demands of the
hydromethanation
reaction.
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